Beamforming optimization for segmented thin-film acoustic imaging systems incorporated in personal portable electronic devices

ABSTRACT

An acoustic imaging system coupled to an acoustic medium to define an imaging surface. The acoustic imaging system includes an array of piezoelectric acoustic transducers formed at least in part from a thin-film piezoelectric material, such as PVDF. The array is coupled to the acoustic medium opposite the imaging surface and formed using a thin-film manufacturing process over an application-specific integrated circuit that, in turn, is configured to leverage on or more beamforming scan operations to drive the array of piezoelectric actuators to generate an image of an object at least partially wetting to the imaging surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a nonprovisional of, and claims the benefit under 35U.S.C. 119(e) of, U.S. Provisional Patent Application No. 63/169,040,filed Mar. 31, 2021, the contents of which are incorporated herein byreference as if fully disclosed herein.

TECHNICAL FIELD

Embodiments described herein relate to digital imaging systems and, inparticular, to acoustic imaging systems and methods for operating thesame configured for use through an exterior surface having an arbitraryprofile (e.g., curved, planar, and so on) of a portable electronicdevice, such as a display surface or a housing surface of a handheld,personal electronic device.

BACKGROUND

An acoustic imaging system can be used to capture an image of an objectat least partially wetting to a surface, often referred to as an“imaging surface.” Certain conventional acoustic imaging systems areimplemented with a two-dimensional array of microelectromechanicalpiezoelectric actuators that (1) generate an acoustic pulse directedtoward the imaging surface in response to stimulus from controlelectronics and/or (2) output an electrical signal upon receivingreflections of those acoustic pulses resulting from impedance mismatchboundaries defined by contours of the object wetting to the imagingsurface.

In many cases, however, conventional imaging systems are not suitable tooperate with nonplanar imaging surfaces, such as curved sidewallsurfaces of a button, a housing, or a rotary input device.

SUMMARY

Embodiments described herein relate to signal processing chains forthin-film acoustic imaging systems leveraged by portable electronicdevices for biometric imaging. Specifically, a portable electronicdevice can include an imaging system, as described herein. The imagingsystem can be coupled to (and/or can partially define) a surface of ahousing of the portable electronic device.

For embodiments described herein, the surface may be a flat/planarsurface, such as a display surface, or may be a curved surface such as asidewall surface. In many examples, embodiments described herein areconfigured to leverage adaptive beamforming techniques to (1) improvecontrast uniformity across an imaging surface and (2) to improve overallsignal to noise ratios by automatically reducing carrier noise viadestructive interference.

This architecture and arrangement defines an imaging area that, iftouched by a user, exhibits a pattern of acoustic impedance mismatchthat corresponds to that user's fingerprint. More generally, any objectthat contacts the imaging area causes a pattern of acoustic impedancemismatch that corresponds to surface features of an exterior surface ofthat object that are in contact with (e.g., wetting to) to the imagingarea. In some examples, subsurface acoustic impedance mismatch patternsmay also be introduced.

For certain embodiments described herein, a thin-film acoustic imagingsystem can include an array of imaging tiles, each tile including anarray of independently-addressable thin-film acoustic transducers. Insome examples, although not required, each transducer or at least one ofthe transducers is formed from polyvinylidene fluoride (PVDF) disposedover a semiconductor circuit (e.g., in a spin coating operation).

Each of the independently-addressable thin-film acoustic transducers canbe conductively coupled to one or more drive control electronics (whichcan be defined in whole or in part in the semiconductor circuit). Thedrive control electronics can be configured to apply a high-frequencysignal (e.g., 10 MHz-20 MHz) to at least one of theindependently-addressable thin-film acoustic transducers to cause thatthin-film acoustic transducer to generate an acoustic pulse thatpropagates through at least a portion of the housing of the portableelectronic device toward the imaging area. In many embodiments, multipletransducers can be driven in a particular sequence and/or with specificphase shifts and/or amplitude variations so as to beamsteer and/orbeamform acoustic energy in a particular direction in order toconstructively or destructively interfere at a particular point or setof points. In many cases, a beamforming operation may be spatiallyoptimized in order to reduce carrier noise at a transducer, or set oftransducers, configured to receive reflections resulting from thebeamforming operation.

Reflections from the imaging area thereafter return to the array ofindependently-addressable thin-film acoustic transducers which maygenerate an electrical signal corresponding to a magnitude of acousticenergy received at least respective transducer. As may be appreciated bya person of skill in the art, the magnitude of acoustic energy receivedat each transducer may be a function of the acoustic impedance mismatchpattern introduced by an object, such as a finger, engaging/touching theimaging area.

To receive and process these reflections (e.g., in order to reconstructor otherwise resolve an image of the external surface of the objectengaging the imaging area), the imaging system includes signalprocessing and/or conditioning pipeline and an analog-to-digitalconverter.

More specifically, each tile of the array of imaging tiles is associatedwith a dedicated analog front end responsible for preprocessing and/orconditioning signals received from each thin-film acoustic transducer ofthat tile. Each dedicated analog front end, of each tile of the array oftiles, is coupled to a shared analog to digital converter. As a resultof this architecture, a single high-resolution analog to digitalconverter (e.g., a successive approximation analog to digital converter)can be used to convert output signals from eachindependently-addressable thin-film acoustic transducer into a digitalvalue suitable for generating an image of an object in direct orindirect contact with the thin-film acoustic imaging system.

In many embodiments, each analog front end of each tile of the array ofimaging tiles includes a carrier rejection biasing element configured tobias an output of at least one thin-film acoustic transducer in a mannerthat reduces carrier noise in the output signal. In other cases, a lowpass filter or other envelope-based detection/filtering mechanism can beused.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to representative embodiments illustrated inthe accompanying figures. It should be understood that the followingdescriptions are not intended to limit this disclosure to one includedembodiment. To the contrary, the disclosure provided herein is intendedto cover alternatives, modifications, and equivalents as may be includedwithin the spirit and scope of the described embodiments, and as definedby the appended claims.

FIG. 1A depicts an example electronic device incorporating a thin-filmacoustic imaging system defining an imaging surface above an activedisplay area of the electronic device, such as described herein.

FIG. 1B depicts an example electronic device incorporating a thin-filmacoustic imaging system defining an imaging surface along a housingsidewall of the electronic device, such as described herein.

FIG. 1C depicts an example electronic device incorporating a thin-filmacoustic imaging system defining an imaging surface along anotherhousing sidewall of the electronic device, such as described herein.

FIGS. 1D-1I depict an example wearable electronic device incorporating athin-film acoustic imaging system, such as described herein.

FIG. 2A depicts an example simplified system diagram of a thin-filmacoustic imaging system including a rectilinear distribution ofpiezoelectric transducers, such as described herein.

FIG. 2B depicts an example simplified system diagram of a thin-filmacoustic imaging system including a grid distribution of piezoelectrictransducers, such as described herein.

FIG. 2C depicts an example simplified system diagram of the thin-filmacoustic imaging system of FIG. 1A, taken through section A-A, depictingan acoustic wave propagating toward a user's finger wetting to animaging surface.

FIG. 2D depicts the simplified system diagram of FIG. 2C, depicting aset of acoustic wave reflections propagating from impedance mismatchboundaries defined by contours of the user's fingerprint.

FIG. 2E depicts an example simplified system diagram of a thin-filmacoustic imaging system positioned below, and configured to operatewith, a convex imaging surface, such as described herein.

FIG. 2F depicts an example simplified system diagram of a thin-filmacoustic imaging system positioned below, and configured to operatewith, a concave imaging surface, such as described herein.

FIG. 3 depicts an example simplified system diagram of a thin-filmacoustic imaging system, such as described herein.

FIG. 4 depicts an example simplified detail view of a thin-film acousticimaging system, such as described herein (see, e.g., FIG. 1A, takenthrough section A-A), including a thin-film piezoelectric actuator.

FIG. 5 depicts another example simplified detail view of a thin-filmacoustic imaging system, including a thin-film piezoelectric actuatorformed over an application-specific integrated circuit.

FIG. 6A depicts a system diagram of a segmented acoustic imaging system,as described herein.

FIG. 6B depicts a schematic/signal flow diagram of an analog front endof a tile of a segmented acoustic imaging system as described herein.

FIG. 7 depicts a system diagram of a segmented acoustic imaging system,as described herein.

FIGS. 8A-8C depict a simplified cross-section of an acoustic imagingsystem as described herein, implementing a linear scan drive operationthat leverages beamforming to focus acoustic energy emitted frommultiple acoustic transducers at a selected location of a curved imagingsurface.

FIGS. 9A-9B depict a simplified cross-section of an acoustic imagingsystem as described herein, implementing a depth-averaging scan driveoperation that leverages beamforming to focus acoustic energy emittedfrom multiple acoustic transducers at a selected location to a selecteddepth, of a curved imaging surface.

FIGS. 10A-10C depict a simplified cross-section of an acoustic imagingsystem as described herein, implementing a sweep scan drive operationthat leverages beamforming to focus acoustic energy emitted frommultiple acoustic transducers at a set of selected locations of a curvedimaging surface.

FIGS. 11A-11C depict a simplified cross-section of an acoustic imagingsystem as described herein, implementing an inverse sweep scan driveoperation that leverages beamforming to focus acoustic energy emittedfrom multiple acoustic transducers at a selected location of a curvedimaging surface.

FIG. 12 depicts a system/signal flow diagram of a system for optimizingdelay coefficients of a drive mode of an acoustic imaging system asdescribed herein.

FIG. 13 is a flowchart depicting example operations of a method ofoperating a thin-film acoustic imaging system, such as described herein.

FIG. 14 is a flowchart depicted example operations of a method ofoperating a thin-film acoustic imaging system, such as described herein.

The use of the same or similar reference numerals in different figuresindicates similar, related, or identical items.

The use of cross-hatching or shading in the accompanying figures isgenerally provided to clarify the boundaries between adjacent elementsand also to facilitate legibility of the figures. Accordingly, neitherthe presence nor the absence of cross-hatching or shading conveys orindicates any preference or requirement for particular materials,material properties, element proportions, element dimensions,commonalities of similarly illustrated elements, or any othercharacteristic, attribute, or property for any element illustrated inthe accompanying figures.

Similarly, certain accompanying figures include vectors, rays, tracesand/or other visual representations of one or more example paths—whichmay include reflections, refractions, diffractions, and so on, throughone or more mediums—that may be taken by, or may be presented to,represent one or more propagating waves of mechanical energy (herein,“acoustic energy”) originating from one or more acoustic transducers orother mechanical energy sources shown or, in some cases, omitted from,the accompanying figures. It is understood that these simplified visualrepresentations of acoustic energy are provided merely to facilitate anunderstanding of the various embodiments described herein and,accordingly, may not necessarily be presented or illustrated to scale orwith angular precision or accuracy, and, as such, are not intended toindicate any preference or requirement for an illustrated embodiment toreceive, emit, reflect, refract, focus, and/or diffract acoustic energyat any particular illustrated angle, orientation, polarization, color,or direction, to the exclusion of other embodiments described orreferenced herein.

Additionally, it should be understood that the proportions anddimensions (either relative or absolute) of the various features andelements (and collections and groupings thereof) and the boundaries,separations, and positional relationships presented therebetween, areprovided in the accompanying figures merely to facilitate anunderstanding of the various embodiments described herein and,accordingly, may not necessarily be presented or illustrated to scale,and are not intended to indicate any preference or requirement for anillustrated embodiment to the exclusion of embodiments described withreference thereto.

DETAILED DESCRIPTION

Embodiments described herein relate to acoustic imaging systems and, inparticular, to acoustic imaging systems incorporated into electronicdevices leveraged to capture images of fingerprints of users of thoseelectronic devices.

In particular, embodiments described herein reference methods operatingan acoustic imaging system that includes an array of acoustictransducers (which may be thin-film acoustic transducers), as describedherein, that leverage beamforming and/or beamsteering techniques tocondition or concentrate acoustic energy output from each of a first setof acoustic transducers of the array of acoustic transducers toward aselected fractional area of an imaging surface defined by the acousticimaging system.

More specifically, embodiments described herein reference systems andmethods for driving multiple acoustic transducers withdifferently-phased signals and/or at different times (e.g., withdifferent delay) so that acoustic energy output from two or moreacoustic transducers constructively or destructively interfere at aparticular location of an imaging surface or at a particular locationafter having reflected from the imaging surface. For example, in someembodiments, beamforming may be used to reduce carrier noise atsense-mode transducers; in such examples, delay coefficients that definedelays and/or phase relationships between different drive-modetransducers may not be optimized to concentrate acoustic energy at theimaging surface but, rather, may be optimized to reduce carrieramplitude observed by sense-mode transducers that receive acousticenergy having been reflected from the imaging surface at least once.

More generally, for embodiments described herein, beamforming may beleveraged to improve image contrast and/or increase signal to noiseratio(s). In such examples, selected drive-mode transducers can beoperated according to implementation-specific delays/phases in order toeffect a particular increase or decrease of acoustic energy at aparticular location, which may be at an imaging surface or, in othercases, at one or more selected sense-mode transducers.

Embodiments described herein can be further configured for higher-ordercontrol of beamforming operations. For example, a particular or selectedbeamforming operation can be executed to obtain a digital or analogvalue corresponding to an acoustic impedance mismatch at a particularfractional area of an imaging surface. By interactively or progressivelychanging which fractional area (e.g., in rows or columns) of an imagingsurface is the target of the beamforming operation, a two-dimensionalimage of an object wetting to the imaging surface can be constructed.For example, if a user is touching the imaging surface with a finger, animage of the user's fingerprint can be generated leveraging the systemsand methods described herein.

For example, in one embodiment, an imaging surface can be subdividedinto 1024 fractional segments, arranged in 16 rows of 64. In thisexample, an acoustic imaging system can leverage a beamforming operationto target one fractional area at a time, progressively building an imageof an object engaging the surface, the image being 16×64 pixels inresolution.

In another examples, an imaging surface can be logically subdivided into66,560 fractional segments, arranged in 64 rows of 1024. In thisexample, an acoustic imaging system can leverage a beamforming operationto target one fractional area at a time, progressively building an imageof an object engaging the imaging surface, the image being 64×1024pixels in resolution.

These foregoing examples are not limiting; any suitable number offractional subdivisions of an imaging surface can be defined by a systemas described herein.

Similarly, it may be appreciated that a manner in which an acousticimaging system advances from one selected fractional area of the imagingsurface to another fractional area of the imaging surface can vary fromembodiment to embodiment. For example, in some cases, fractional areascan be sampled row-wise, column-wise, randomly, in a checker-boardpattern, in a serpentine pattern, in a concentric pattern, and so on. Insome cases, a single fractional area may be imaged using two or moredifferent beamforming operations. In such cases, individual measurementsor imaging results can be averaged and/or combined in another suitableway. It may be appreciated that these examples are not exhaustive; anysuitable technique for scanning and/or rasterizing an image of theimaging surface may be used.

As such, for simplicity of description, many embodiments describedherein reference a plan scanner configured to select or otherwisedetermine a scan plan. A scan plan can be associated with a particularpattern of advancing between fractional areas of an imaging surface. Inaddition, a scan plan can be configured to associated particularfractional areas with particular beamforming operations. For example, insome cases, fractional areas of an imaging surface nearby an edge orperimeter of the imaging surface may be imaged by leveraging a firstbeamforming operation or combination of a set of beamforming operationswhich may be different from a second beamforming operation or secondcombination of beamforming operations leveraged to image a fractionalarea of the imaging surface within a center of the imaging surface.

More particularly, a scan plan as described herein can also define how aparticular beamforming operation should be carried out given aparticular targeted fractional area of the imaging surface. For example,as noted above, for any given beamforming operation, differentdrive-mode transducers may be driven at different times, at differentphases, and/or with different drive signals altogether. As such, a scanplan can include a set of delay coefficients and/or otheroperation-defining parameters or attributes that configure a set ofdrive-mode transducers to provide output in a particular waycorresponding to the desired beamforming operation. As a result of theseand related constructions, a scan planner can be configured to select ascan plan and execute that scan plan which, in turn, causes a process toinitiate that sequentially executes particularly-configured beamformingoperations each uniquely configured to target a particular fractionalarea of the imaging surface. Sense-mode transducers capture reflectionsresulting from each of these beamforming operations and, based on outputfrom the sense-mode transducers, an image of an object engaging theimaging surface can be generated at higher resolution and highercontrast than conventional imaging techniques.

Broadly, an acoustic imaging system as described herein can include ascan planner that is configured to, in response to an instruction togenerate an image of an object engaging an imaging surface, selectand/or determine a scan plan that, in turn, leverages one or morebeamforming techniques to image each among a set of fractional areas ofthe imaging surface. Example scan plans include, but are not limited to:row-wise advancement between fractional areas of the imaging surface;column-wise advancement between fractional areas of the imaging surface;serpentine advancement between fractional areas of the imaging surface;arbitrary patterns of advancement between fractional areas of theimaging surface; random selection of fractional areas of the imagingsurface; arbitrarily-sized region-by-region advancement betweenfractional areas of the imaging surface; and so on. Beamformingoperations leveraged while executing these or other scan plans caninclude: operations in which different frames of delay profiles and/ordelay coefficients are provided to the same set of drive-modetransducers, thereby causing a focal point of acoustic energy to changeframe-by-frame to different fractional areas of the imaging surface;operations in which the same delay profiles are provided in sequence todifferent sets of drive-mode transducers, thereby causing a focal pointof acoustic energy to change frame-by-frame to different fractionalareas of the imaging surface; operations in which different frames ofdelay profiles and/or delay coefficients are provided to the differentsets of drive-mode transducers, thereby causing a focal point ofacoustic energy to remain directed to the same fractional area of theimaging surface; operations in which different frames of delay profilesand/or delay coefficients are provided to the different sets ofdrive-mode transducers, thereby causing a focal point of acoustic energyto change depth relative to the imaging surface but remain directed tothe same fractional area of the imaging surface; and so on. In manycases, as noted above, a single fractional area of the imaging surfacemay be imaged multiple times, in many cases, so that differentbeamforming operations can be performed to the same fractional area. Inthese examples, different measurements can be averaged or combined (orsorted, selected from) in any suitable way.

More generally, it may be appreciated that an acoustic imaging system asdescribed herein can be readily adapted for incorporation in any numberof suitable structures. For example, the beamforming and scan planningoperations described above can enable an acoustic imaging system asdescribed herein to capture an image through curved surface, such as acurved sidewall surface of an electronic device housing.

Similarly, an acoustic imaging system as described herein can beconfigured to capture an image through any suitable material, includingmetals, ceramics, and glass. In many embodiments, an acoustic imagingsystem may be leveraged by an electronic device to capture an image of afingerprint of a user of that electronic device, but this is notrequired of all embodiments and other purposes may be suitable.

In many implementations, an acoustic imaging system, such as describedherein, is positioned behind a display of an electronic device tofacilitate through-display imaging of a user's fingerprint when thatuser touches the display. In other implementations, an acoustic imagingsystem, such as described herein, can be positioned relative to ahousing of a hand-held electronic device to facilitate through-housingimaging of a user's fingerprint when that user handles the hand-heldelectronic device, such as by grasping a sidewall surface of thehousing.

In yet other implementations, an acoustic imaging system, such asdescribed herein, can be positioned relative to a physical input device,such as a button (e.g., a power button) or crown, or key (e.g., of akeyboard), to facilitate imaging of a user's fingerprint when that userinteracts with the physical input device. In still other examples, anacoustic imaging system, such as described herein, can be incorporatedinto any suitable location of any suitable electronic device andleveraged for any suitable imaging purpose, whether biometric orotherwise. These preceding examples are not exhaustive.

For example, an imaging system can be used for input sensing and/orsession management. For example, a fingerprint my be recognized ashaving moved over time (e.g., which may be interpreted as an input)and/or a fingerprint or surface contact image (e.g., from a hand, glove,wrist, and so on) may be recognized as having recently changed by atleast a threshold amount, indicating that a user of the electronicdevice has changed. In this example, active sessions (e.g., websessions) may be invalidated. Many examples and use cases for an imagingsystem as described herein are possible.

For simplicity of description, embodiments described herein reference anacoustic imaging system including a two-dimensional array ofpiezoelectric actuators that may be coupled to an “acoustic medium.” Inmany examples, an acoustic medium as described herein, may be a portionof a housing of an electronic device. In other cases, the acousticmedium may be a liquid or gas, such as air.

In some examples, an acoustic medium defined through an electronicdevice housing can exhibit a generally rectangular cross-sectionalprofile defined by two substantially parallel opposing surfaces, such asan interior surface of the housing and an exterior surface of thehousing. In other cases, an acoustic medium defined through anelectronic device housing can exhibit a curved cross-sectional profiledefined by a planar surface opposite a curved surface, such as a planarinterior surface of the housing and a curved exterior surface of thehousing. Many implementations are possible.

In many examples, a two-dimensional array of piezoelectric actuators isadhered, via a thin layer of impedance-matching adhesive (e.g.,micrometer scale, for example 1-5 μm) to one acoustic medium surface,thereby defining an opposite surface surface as an “imaging surface.”For example, if a thin-film piezoelectric actuator is coupled to aninterior surface of an electronic device housing, a portion of theexterior surface of that electronic device housing opposite thethin-film piezoelectric actuator defines the imaging surface. In thisexample, the material of the housing (e.g., metal, plastic, glass,ceramic, and so on) defines the acoustic medium.

As may be appreciated by a person of skill in the art, a piezoelectricactuator can be manufactured in a number of suitable ways. In someconventional systems, a piezoelectric actuator can be formed in amicroelectromechanical machining process that defines a vacuum cavitybacking a sheet of piezoelectric material. If a voltage is appliedacross the piezoelectric material, the material can compress or expandin a direction, thereby generating a pulse of mechanical energy that canpropagate through any acoustic medium to which the actuator is coupled.

However, manufacturing a microelectromechanical piezoelectric actuatoris a multistage process that is expensive, time consuming, and subjectto substantial error. For example, in many cases, forming vacuumcavities suitable for a large array of acoustic transducers requires aprocess that is incompatible with CMOS processes necessary to define oneor more circuits or traces. As a result, different manufacturing stepsare required which, in turn, requires at least one alignment step duringmanufacturing. As may be appreciated by a person of skill in the art,alignment operations during manufacturing increase rejection rates andnecessitate high tolerance for error, which informs and impacts overalldesign.

To account for these and other issues with conventional acoustic imagingsystems, embodiments described herein leverage thin-film layers thatexhibit piezoelectric properties to define arrays of acoustictransducers. Such layers can be formed over existing integratedcircuits, which in turn means that transducer layers can be formed in asingle contiguous process with CMOS layers, eliminating any need forrepositioning or realignment.

In addition, as a result of the thin-film architecture(s) describedherein, a requirement for a backing layer (such as a vacuum cavity,required of conventional microelectromechanical piezoelectric actuators)is eliminated and, thus, acoustic impedance of a two-dimensional arrayof piezoelectric actuators can be increased relative to conventionalmicroelectromechanical designs. As a result of increased acousticimpedance of the thin-film piezoelectric actuators, an acoustic imagingsystem such as described herein can be closer to impedance matched tomaterials with high acoustic impedance, such as glass or metal,substantially more effectively than conventional acoustic imagingdesigns.

In a more general, non-limiting, phrasing, an acoustic imaging systemsuch as described herein can be used to capture images of objectswetting to imaging surfaces defined by high-impedance materials,exhibiting increased power efficiency and increased signal-to-noiseratio. As a result, an acoustic imaging system such as described hereincan be leveraged by, as one example, a portable electronic device tocapture an image of a user's fingerprint through glass and/or metal,such as may be used to form a housing of the electronic device.

As a result of these described constructions, one or more of thethin-film piezoelectric actuators can generate an acoustic pulse towardthe imaging surface through a body or bulk of the acoustic medium. Asthe propagating acoustic pulse reaches the imaging surface, whichdefines an acoustic boundary, a portion of the acoustic pulse mayreflect back towards the array and a portion of the acoustic pulse maytraverse the acoustic boundary and propagate into another acousticmedium interfacing the imaging surface (e.g., air, an object wetting tothe imaging surface, and so on). This boundary is an acoustic impedancemismatch boundary.

The acoustic imaging system, in these and other related examples, canquantify properties of said reflections by sampling voltages output fromone or more thin-film piezoelectric transducers of the two-dimensionalarray.

In particular, output voltage samples over time may correspond toamplitude of the reflections, which, in turn, can be correlated to theacoustic impedance of the object (and, in particular, the acousticimpedance mismatch between the acoustic medium and the object) wettingto the imaging surface. For example, in the case of a user's fingerprinttouching the imaging surface, ridges of the user's fingerprint introducea different acoustic impedance mismatch than the acoustic impedancemismatch introduced by air enclosed by a valley of the user'sfingerprint.

As a result of this arrangement, the acoustic imaging system can beleveraged to generate an image of acoustic impedance mismatches definedby contours of an object at least partially wetted to the imagingsurface.

For example, the acoustic imaging system may drive individual thin-filepiezoelectric transducers to generate acoustic pulses (e.g., by drivingthe transducers with a wavelet or other electrical signal, such ascurrent or a voltage signal) and receive reflections resulting therefromin a sequence or pattern (e.g., row by row, column by column, transducerby transducer, serpentine pattern, and so on).

In other cases, multiple transducers can be driven or stimulated bycontrol electronics according to a specific timing pattern (e.g.,beamforming) such that multiple acoustic pulses generated by multipletransducers constructively interfere at a target location of the imagingsurface. These preceding examples are not exhaustive; it may beappreciated that a two-dimensional array of piezoelectric transducerssuch as described herein can be leveraged in a number of suitable waysto generate an image, such as described herein.

Further to the foregoing, a thin-film piezoelectric transducer array,such as described herein, can be formed directly atop, over, or anapplication-specific integrated circuit (“integrated circuit”)configured to stimulate selected piezoelectric transducers of the arraywith a voltage to cause each stimulated piezoelectric transducer toexpand along an axis parallel to an electric field within thattransducer induced by the stimulus voltage.

This operation is referred to herein as “driving” a piezoelectrictransducer configured in an “integration mode.” In addition, anapplication-specific integrated circuit is configured to receive andsample, from selected piezoelectric transducers of the array, an outputvoltage resulting from compression or expansion of that respectivepiezoelectric transducer. This operation is referred to herein as“sensing” with a piezoelectric transducer configured in a “sense mode.”

Similarly, it is appreciated that an acoustic medium, such as describedherein, may in some embodiments form a part of an electronic devicedisplay or housing. In such examples, the imaging surface can be anysuitable external surface of an electronic device, such as an externalsurface above a display or an external surface of a housing sidewall.

As a result of this construction, the application-specific integratedcircuit can initiate a drive operation with one or more piezoelectrictransducers configured in an integration mode to generate one or moreacoustic waves.

In further examples, specific signal processing pipelines are describedthat can improve signal to noise ratios when operating in a sense mode.In particular, in many embodiments, an array of thin-film piezoelectricactuators can be subdivided and/or segmented into segments also referredto as “tiles.” Each tile can include dedicated readout circuitry,referred to herein as an “analog front end.” Each analog front end ofeach tile can be configured to perform one or more signal conditioningand/or noise reduction operations such as filtering operations (e.g.,bandpass, high-pass, low-pass, or other frequency-domain filteringoperations), integration operations, amplification operations,attenuation operations, and so on.

Thereafter, outputs from each of the respective analog front ends can bereadout by a shared final stage (or stages) that optionally filtersadditionally and/or converts analog signals to digital values. As aresult of this architecture, a single high-quality analog to digitalconverter with high resolution can be leveraged to convert analogsignals from each individual acoustic transducer of the array ofacoustic transducers. Similarly, signal conditioning operations can beperformed with higher-quality and higher-fidelity circuits andelectronics at the tile level. In these embodiments, benefits associatedwith including high quality components can be balanced against the costof providing high quality signal processing and conditioning pipelinesfor all or substantially all transducers of an array. In addition, thetiled/segmented architecture described herein can be leveraged forparallel processing; while one tile is performing integration and/orsensing operations, other tiles can be performing the same or differentintegration and/or sensing operations. In such cases, analog valuesoutput from one or more of the tiles can be stored in temporary storage(e.g., capacitors) until the shared final stage is available to convertsuch values into digital values suitable for digital-domain digitaloperations such as image construction, contrast correction, templatematching, de-noising, de-skewing, and so on.

These foregoing and other embodiments are discussed below with referenceto FIGS. 1A-10 . However, those skilled in the art will readilyappreciate that the detailed description given herein with respect tothese figures is for explanation only and should not be construed aslimiting.

Generally and broadly, FIGS. 1A-1C depict example electronic devicesthat can incorporate an acoustic imaging system such as describedherein. In particular, as noted above, embodiments described hereinrelate to acoustic imaging systems that resolve an image of an objectengaging an imaging surface (also referred to as an input surface) of anelectronic device by generating acoustic pulses (one or more; in someexamples constructively interfering via beamforming and/or phased arrayexcitation techniques) with piezoelectric acoustic transducers.

The acoustic pulses propagate through a portion of the housing of theelectronic device (more generally referred to herein as the “acousticmedium”) toward the imaging surface and, thereafter, the acousticimaging system samples voltage signals produced by the same or differentpiezoelectric acoustic transducers to quantify reflections of theacoustic pulses from the imaging surface.

As may be appreciated by a person of skill in the art, amplitudes ofreflections from the imaging surface correspond to acoustic impedancemismatch boundaries at the imaging surface; some objects wetting to theimaging surface may absorb more acoustic pulse energy (e.g., objectshaving an acoustic impedance close to that of the acoustic medium) thanother objects wetting to the imaging surface (i.e., objects having anacoustic impedance substantively different from that of the acousticmedium).

By iteratively generating acoustic pulses at any suitable waveform orcarrier frequency and characterizing reflections resulting therefrom, anacoustic imaging system, such as described herein, can be leveraged togenerate a two-dimensional image (or in further examples athree-dimensional image) the contrast of which corresponds to acousticimpedance mismatch boundaries/contours of one or more objects wetting tothe imaging surface.

In one particular example, an acoustic imaging system may be used togenerate an image of a fingerprint wetting to an imaging surface.Portions of that fingerprint that directly wet to the imaging surface(e.g., ridges) may reflect a different quantity of acoustic energy thanportions of that fingerprint that do not wet to the imaging surface(e.g., valleys).

As such, different acoustic impedance mismatches are associated withridges and valleys of a user's fingerprint and, by mapping acousticimpedance mismatch at different locations of the imaging surface, atwo-dimensional image of the user's fingerprint can be generated which,in turn, can be computer readable and may be leveraged by the electronicdevice to perform a particular function, such as authentication oridentification or a particular user.

For simplicity of description, many embodiments described herein areconfigured to operate as (or with) a biometric sensor that obtains andanalyzes an image of a user's fingerprint when the user touches adisplay of an electronic device with one or more fingers. It isappreciated, however, that although many embodiments are describedherein with reference to obtaining an image of a user's fingerprint, thevarious systems and methods described herein can be used to performother operations, or to obtain non-fingerprint information, such as, butnot limited to: obtaining an image of a palm; obtaining an image of anear or cheek; determining the location of a stylus on an imaging surfaceof an electronic device; determining a physiological characteristic of auser such as heart rate or blood oxygenation; determiningcharacteristics of a non-imaging surface; determining the force withwhich a user touches an imaging surface; determining the location atwhich a user touches an imaging surface; determining a user touch orforce input to an imaging surface; and so on.

Accordingly, it may be appreciated that the various systems and methodspresented below are merely examples and that other embodiments, systems,methods, techniques, apparatuses, and combinations thereof arecontemplated in view of the disclosure provided below.

As used herein, the term “image” and the phrase “resolved image” refersto a collection of pixels, the coordinates of which correspond to localsurface characteristics of an acoustic medium (or a portion thereof)that may change as a result of a user's fingertip when the fingertipmakes physical contact with the acoustic medium at that location.

The area over which a user's fingertip contacts the acoustic medium canbe referred to herein as the “contact area.”

Typically, the acoustic medium defines an imaging surface of anelectronic device such as, but not limited to: a touch-sensitivesurface; a touch-sensitive display; a force-sensitive surface; aforce-sensitive display; a cover glass of a display; an exterior surfaceof a housing or enclosure such as a protective outer layer; a sidewallsurface of an electronic device; a button surface of an electronicdevice; a curved sidewall of an electronic device; a side or endcapsurface of a rotary input device; and so on. In these embodiments, thecontact area typically takes the shape of a pad of a user's fingertip(e.g., an ellipse).

In many embodiments, each pixel of a resolved image corresponds to anattenuation experienced by a reflection of an acoustic pulse propagatingto, and reflecting from, that respective pixel location. The amount ofattenuation (e.g., an “attenuation coefficient”) at a particularlocation corresponds to a value (e.g., darkness, lightness, color,brightness, saturation, hue, and so on) of the associated pixel of theresolved image.

For example, the attenuation coefficient may be a number from 0 to 1.0,and the corresponding pixel may include a brightness value from 0 to 255units. In this example, the attenuation coefficient and the brightnessof the corresponding pixel value may be linearly related, although sucha relationship is not necessarily required of all embodiments.

The resolution of the resolved image (and thus the number and/ordistribution of pixels forming the same) can be based, at least in part,on the expected or average size of various features of the user'sfingerprint. In one example, the resolution of the resolved image isgreater than 120 pixels per centimeter (approximately 300 pixels perinch). In further examples, the resolution of the resolved image isgreater than or equal to 200 pixels per centimeter (approximately 500pixels per inch). In still further examples, other resolutions may besuitable. In some cases, the resolution of the resolved image may benon-uniform; certain areas of the resolved image may have a higherresolution than other areas.

As may be appreciated, and as noted above, an attenuation coefficientassociated with a particular location of the acoustic medium (e.g., a“local attenuation coefficient”) changes when a fingertip (or moreparticularly, a “feature” of a fingertip such as a ridge or a valley) isin physical contact with, or otherwise “wets” to, the acoustic medium(e.g., metal, plastic, glass, and so on) at that specific location. Thisis due to an acoustic impedance mismatch introduced by the wetting ofthe fingertip (or feature) to the acoustic medium at that location.

As noted above, the term “wetting” and related terminology refers to thespreading and/or partial compression of an object (often a solid objectsuch as a finger), or the outermost surface of the same, when the objectphysically contacts or touches a surface. For example, a fingertip wetsto the surface of the acoustic medium when the user presses thefingertip against the acoustic medium, causing the ridges of thefingerprint to compress and spread by a certain amount, therebydisplacing substantially all air between the ridges of the fingerprintand the surface of the acoustic medium,

For example, as noted above, a feature of a fingertip in direct physicalcontact with the acoustic medium at a particular location (e.g., a ridgeof a fingerprint) attenuates an acoustic pulse propagated toward it,thereby affecting the value of the associated pixel of the resultingimage.

Conversely, a feature that does not wet to the surface of the acousticmedium (e.g., a valley of a fingerprint) may not substantially attenuateacoustic pulses propagated therethrough, similarly not affecting thevalue of the associated pixel of the resulting image.

In this manner, the value of each pixel of the resolved imagecorresponds to whether or not a feature of a fingertip is wetted to theacoustic medium at that pixel location. More specifically, the pixels ofthe resolved image correspond to whether a ridge or a valley of a user'sfingerprint is present at that pixel location. In this manner, theresolved image may serve as a direct proxy for an image of the user'sfingerprint.

Furthermore, different features of a fingertip may introduce differentacoustic impedance mismatches, thus resulting in different localattenuation coefficients and different pixel values in the resolvedimage.

For example, denser features of the fingertip (e.g., scar tissue) wettedto the acoustic medium may change local attenuation coefficient(s)differently than less dense features wetted to the surface of theacoustic medium. In other cases, the force with which the user touchesthe acoustic medium may affect local attenuation coefficients bycompressing the fingertip against the acoustic medium. In this manner,the resolved image may exhibit contrast corresponding to the relativedensity of features of the fingertip wetted to the acoustic medium.

Accordingly, generally and broadly, an acoustic imaging system such asdescribed herein is configured to resolve an image of a user'sfingerprint by resolving an image of the acoustic attenuation effectsprovided by various features of the fingertip that make physical contactwith the acoustic medium at various location. Such an image may bereferred to herein as an “acoustic attenuation map” of an acousticmedium or contact area.

In some embodiments, an acoustic attenuation map can be modeled as amatrix, a vector, or as a function, the inputs of which are coordinatesthat correspond to locations on the acoustic medium. It may beappreciated that an acoustic imaging system such as described herein canobtain, resolve, or estimate an acoustic attenuation map of an acousticmedium (or contact area of the acoustic medium) using any suitable orimplementation-specific method or combination of methods, several ofwhich are described in detail below.

FIG. 1A depicts an electronic device 100 a incorporating a thin-filmacoustic imaging system defining an imaging surface above an activedisplay area of the electronic device, such as described herein.

As depicted, an electronic device 100 a can be implemented as a portableelectronic device such as a cellular phone, although such animplementation is not required and other embodiments may be implementedas, without limitation: input devices; laptop computers; desktopcomputers; industrial processing interfaces; home automation devices;industrial security devices; navigation devices; peripheral inputdevices; and so on.

As may be appreciated, for simplicity of illustration, the electronicdevice 100 a is depicted without many elements and functional componentsthat may be leveraged by the electronic device to perform variousoperations, including operations related to an acoustic imaging system,such as described herein. For example, although not depicted, it may beappreciated that the electronic device 100 a can include one or moreprocessors, one or more memory elements, one or more data stores, one ormore input components or sensors, and so on.

As described herein, the term “processor” refers to any software and/orhardware-implemented data processing device or circuit physically and/orstructurally configured to instantiate one or more classes or objectsthat are purpose-configured to perform specific transformations of dataincluding operations represented as code and/or instructions included ina program that can be stored within, and accessed from, a memory. Thisterm is meant to encompass a single processor or processing unit,multiple processors, multiple processing units, analog or digitalcircuits, or other suitably configured computing element or combinationof elements.

In many embodiments, the processor can be operably coupled to a workingmemory and/or a long term memory. In these examples, a memory of theelectronic device 100 a can be configured to store at least oneexecutable asset that, when accessed from the memory by the processor(and/or loaded into the working memory by the processor) can instantiatean instance of software configured to leverage and/or integrate with anacoustic imaging system as described herein. Such instances of softwarecan be configured for any suitable purpose.

The electronic device 100 a also includes a housing 102 and a display104 defining an active display area 106. The display 104 is disposedbelow a protective outer layer to protect the display 104 from damage.In this manner, the protective outer layer above the display forms aportion of the housing 102, defining an exterior surface thereof. Inmany cases, the protective outer layer can be formed from an opticallytransparent and mechanically rigid material such as glass, sapphire,polycarbonate, and so on.

In many embodiments, the protective outer layer protecting the display104 can be manufactured, at least in part, from a material exhibiting ahigh acoustic impedance, such as glass, crystalline materials, ortransparent ceramic. In this context, “high” acoustic impedance refersto materials having an acoustic impedance greater than air and/orgreater than organic material, such as a user's finger.

In many embodiments, an acoustic imaging system 108 can be disposedwithin the housing 102 of the electronic device 100 a. As with otherembodiments described herein, the acoustic imaging system 108 caninclude an array of acoustic transducers that are configured to generateacoustic pulses and to receive reflections (e.g., echoes) thereof.

For example, in some embodiments, the acoustic imaging system 108 can becoupled to (e.g., adhered) an internal surface the protective outerlayer of the display 104. As a result of this construction, the acousticimaging system 108 can be leveraged to resolve an image of an object,such as the pad of a fingertip (e.g., fingerprint) of a user 110, inphysical contact with the protective outer layer. More particularly, theacoustic imaging system 108 can be configured to determine an acousticattenuation map of an imaging surface defined as a portion of anexterior surface of the protective outer layer of the display 104.

In some cases, the acoustic imaging system 108 is configured to generateand/or estimate an acoustic attenuation map of only a portion of theprotective outer layer of the display 104. This may increase the speedwith which the acoustic attenuation map may be generated and/orestimated by reducing the number of calculations and/or operationsrequired. In the illustrated embodiment, the portion of the protectiveouter layer is identified with a dotted line enclosing a rectangulararea. In other examples, other area shapes are possible.

Once an image of fingerprint (or other biometrically-unique surfacecharacteristics such as handprints, ear prints, and so on) of the user110 is imaged by the acoustic imaging system 108, the obtained image canbe compared to a database of known images to determine if the obtainedimage, and/or features or information derived therefrom (e.g., vectormaps, hash values, and so on), matches a known image.

If an affirmative match (e.g., a match exceeding or otherwise satisfyinga threshold) is obtained, the electronic device 100 a can perform afunction related to the match. In one example, the electronic device 100a performs a privacy-sensitive authenticated function, such asdisplaying financial information on the display 104.

In other embodiments, an acoustic imaging system, such as the acousticimaging system 108 may be disposed relative to other portions of thehousing 102 of the electronic device 100 a, so as to defined imagingsurfaces elsewhere than shown in FIG. 1A. For example, FIG. 1B depictsan example configuration in which an acoustic imaging system 108 can bepositioned relative to a sidewall of the electronic device 100 b, suchthat a fingerprint image of a user 110 can be captured while the user110 grasps the phone.

In another example depicted in FIG. 1C, an acoustic imaging system 108,such as described herein, can be disposed along a sidewall of a housing102 of the electronic device 100 c. In contrast to FIG. 1B, in FIG. 1C,the acoustic imaging system 108 can extend for substantially an entirelylength of a sidewall of the housing 102 of the electronic device 100 c.As a result of this construction, multiple fingerprint images can becaptured simultaneously, such as the user's fingerprint 110 a and theuser's fingerprint 110 b.

These foregoing embodiments depicted in FIGS. 1A-1C and the variousalternatives thereof and variations thereto are presented, generally,for purposes of explanation, and to facilitate an understanding ofvarious configurations and constructions of a system, such as describedherein. However, it will be apparent to one skilled in the art that someof the specific details presented herein may not be required in order topractice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions ofspecific embodiments are presented for the limited purposes ofillustration and description. These descriptions are not targeted to beexhaustive or to limit the disclosure to the precise forms recitedherein. To the contrary, it will be apparent to one of ordinary skill inthe art that many modifications and variations are possible in view ofthe above teachings.

For example, it may be appreciated that any number of acoustic imagingsystems can be included in an electronic device, such as describedherein. Such systems can be associated with any internal or externalsurface of an electronic device; some constructions may position anacoustic imaging system adjacent to a sidewall surface of an electronicdevice, whereas others may position an acoustic imaging system below orrelative to an active display area of a display.

It is appreciated that any suitable number of configurations andconstructions are possible in view of the description provided herein.

For example, FIGS. 1D-1I depict an example set of embodiments in whichan acoustic imaging system, such as described herein, can beincorporated into various portions of a wearable electronic device suchas a smart watch secured to a wrist of a user by a band. As noted above,this is merely one example of an electronic device or, more generally,one example of a wearable electronic device, and it may be appreciatedthat other constructions and architectures are possible in view of theembodiments described herein.

For example, FIG. 2D depicts a wearable electronic device 100 d thatincludes a housing 112 enclosing and supporting operational andfunctional components of the wearable electronic device 100 d. Thehousing 112 can be formed from any suitable material including plastics,metals, ceramics, glass, and so on. The housing 112 can be rigid orflexible and may be monolithic or formed from multiple discretesections, layers, or portions of material—which may be the same materialor differing materials—and may take any suitable shape. The housing 112can have rounded or flat sidewalls.

The housing 112 can be secured to a limb of a wearer, such as a wrist,by a band 114. The band 114 can be flexible or rigid and can be formedfrom any suitable material or combination of materials. The band 114 canbe formed from, and/or defined by, a single piece of material ormultiple interlocking or interwoven pieces of material. The band 114 canbe configured to stretch, flex, and/or bend around or contour to auser's wrist in any suitable manner.

The housing 112 can enclose a display that can be used to render agraphical user interface within an active display area 116 configured toemit light through at least a portion of the housing 112. In someexamples, a display defining the active display area 116 can bepositioned below a cover glass that defines at least a portion of anexterior surface of the housing 112.

As with other embodiments described herein, the wearable electronicdevice 100 d can incorporate acoustic imaging system that may beconfigured in the same manner as described above with respect to FIGS.1A-1C.

In FIG. 1D, the acoustic imaging system is identified as the acousticimaging system 108. In this illustration, the acoustic imaging system108 is disposed relative to the active display area 116 such that when auser 110 interacts with content rendered in the graphical user interfaceshown by the active display area 116 of the display of the wearableelectronic device 100 d, the acoustic imaging system 108 can operate todetect and/or image a fingerprint of the user 110.

The depicted configuration is merely one example; the acoustic imagingsystem 108 can be disposed in any suitable portion of a wearableelectronic device such as described herein. For example, FIG. 1E depictsa configuration in which a wearable electronic device 100 e includes theacoustic imaging system 108 across only a portion of the active displayarea 116 of the wearable electronic device 100 e.

In other cases, an acoustic imaging system 108 can be included in atleast a portion of the band 114, such as shown in FIG. 1F. In thisembodiment, a user 110 that touches an exterior surface of the band 114can engage the acoustic imaging system 108 which, in response, cangenerate an image of the user's fingerprint. In yet other examples, theacoustic imaging system 108 can be configured to image a surface of thewrist of the user 110.

In other words, in some configurations, the acoustic imaging system 108can be oriented to direct acoustic imaging functionality toward theuser's wrist. In some examples of these configurations, the acousticimaging system 108 can be configured to detect and/or identify one ormore skin characteristics of the epidermis of the wearer (e.g., the user110). In other examples of these configurations, the acoustic imagingsystem 108 can be configured to image subdermal layers of the user'swrist, for either biometric imaging purposed or biometric datacollection purposes. For example, in some examples, an acoustic imagingsystem 108 as described herein that is incorporated into a band 114and/or a housing of a wearable electronic device such as the wearableelectronic devices 100 d, 100 e, or 100 f can be configured to generatean acoustic image of an interior of the user's wrist, such as an imageof an artery, a vein pattern, a musculature image, a skeletal image, andso on. Such images, and/or combinations thereof, can be leveraged by thewearable electronic device for authentication purposes and/or biometricdata collection purposes.

In yet other embodiments the acoustic imaging system 108 can beincorporated into an exterior surface a rotating input device extendingfrom and/or integrated with the housing 112. For example, as shown inFIG. 1G, a crown 118 can incorporate the acoustic imaging system 108such that as a user 110 moves his or her finger across the crown toprovide a rotating input to the wearable electronic device 100 g, theacoustic imaging system 108 can become in contact with a progressivelydifferent portion of the user's fingerprint, thereby progressivelybuilding a fingerprint image and/or at least a portion thereof.

In yet further examples, the acoustic imaging system 108 can beincorporated into a sidewall surface of the housing 112. For example,FIG. 1H depicts the acoustic imaging system 108 positioned relative to alateral sidewall of the housing 112, through which physical inputcontrols may likewise extend. For example, as shown in FIG. 1G, a button120 and/or a rotary input device 122 can be included.

Each of these controls may be configured to move and/or rotate inresponse to an application of pressure or friction by a user, such asthe user 110. A degree to which either control moves may be received bythe wearable electronic device as an input. For example, the wearableelectronic device 100 g can receive a degree of rotation of the rotaryinput device 122 as a scrolling input and may receive a press of thebutton 120 as a selection input. These foregoing examples are notexhaustive; any suitable input device whether physical or virtual can beincluded in a wearable electronic device as described herein.

In the illustrated example, the acoustic imaging system 108 isconfigured to provide acoustic imaging functionality through a sidewallportion of the electronic device that is separate from other physical orvirtual controls (e.g., buttons, rotary input devices, and so on)defined through that sidewall; this is merely one example configuration.

For example, in other embodiments, an acoustic imaging system such asthe acoustic imaging system 108 can be included within a physicalcontrol of the wearable electronic device. For example, as shown in FIG.1I, the acoustic imaging system 108 can be included within the rotaryinput device 122. In the illustrated embodiment, the acoustic imagingsystem 108 is disposed to provide acoustic imaging functionality from acircular surface area of the rotary input device 122, but this is alsomerely one example construction. In some examples, the acoustic imagingsystem 108 can be included within and/or disposed around a circumferenceof the rotary input device 122; in this construction, as a user rotatesthe rotary input device 122, a different portion of that user's fingeris in contact with the rotary input device 122, thereby enabling theacoustic imaging system 108 to image a different portion of that user'sfingerprint.

These foregoing embodiments depicted in FIGS. 1D-1I and the variousalternatives thereof and variations thereto are presented, generally,for purposes of explanation, and to facilitate an understanding ofvarious configurations and constructions of a system, such as describedherein. However, it will be apparent to one skilled in the art that someof the specific details presented herein may not be required in order topractice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions ofspecific embodiments are presented for the limited purposes ofillustration and description. These descriptions are not targeted to beexhaustive or to limit the disclosure to the precise forms recitedherein. To the contrary, it will be apparent to one of ordinary skill inthe art that many modifications and variations are possible in view ofthe above teachings.

For example, generally and broadly, it may be appreciated that anacoustic imaging system can take any shape (e.g., rectilinear shapes,circular shapes, square shapes, polygonal shapes, and so on) and can beincorporated into any suitable electronic device or surface or inputcomponent thereof. Further, it may be appreciated that a singleelectronic device can include multiple different and/or discreteacoustic imaging systems. For example, in some embodiments, a firstimaging system may be disposed within a button or rotary input deviceand a second acoustic imaging system may be disposed behind (and/orotherwise relative to) a display of the same wearable, portable, orstationary electronic device.

Generally and broadly, FIGS. 2A-3 depict simplified system diagrams ofan acoustic imaging system, such as described herein. Independent ofwhether the acoustic imaging system of these embodiments is constructedusing d31 or d33 piezoelectric transducers, it may be appreciated thatthe piezoelectric transducers can be coupled to and/or otherwise formedon an application-specific integrated circuit, which in turn may beformed in a reel-to-reel or single-stage thin-film transistormanufacturing process.

As a result of this configuration, an acoustic imaging system such asdescribed herein can be manufactured without a requirement for alignmentof an array of microelectromechanical piezoelectric transducers withsignal traces, solder pads, or other electrical or mechanicalcoupling(s). As such, an acoustic imaging system, such as describedherein, can be manufactured at a more rapid pace and/or can be coupledto an acoustic medium (such as an electronic device housing as shown inFIGS. 1A-1C) to define an imaging surface in a number of suitable ways,several of which are described below.

Further, it may be appreciated that the following (and foregoing)embodiments may be coupled to an acoustic medium with any suitableadhesive or mechanical fastener or fastening methodology (includingfriction fit, insert molding and the like). In many embodiments, as maybe appreciated by a person of skill in the art, an adhesive and/ormechanical fastener used to couple an acoustic imaging system, such asdescribed herein, to a surface of an acoustic medium (e.g., display,housing, sidewall, and so on) can be selected at least in part based onan acoustic impedance of that material (when cured, cooled, or otherwisein a final manufacturing state).

More specifically, in many embodiments adhesives to couple an acousticimaging system to an acoustic medium may be selected and/or depositedand/or cured so as to provide an acoustic impedance transition from anacoustic imaging system (and, in particular, an array of piezoelectrictransducers of an acoustic imaging system) to the acoustic medium.

In this manner, a person of skill in the art will appreciate, that theacoustic imaging system can be more effectively matched to the acousticmedium and, as a result, can more efficiently operate to obtain an imageof an object wetting to the imaging surface, such as a fingerprintwetting to an external surface of an electronic device housing.

For example, and as noted above, embodiments described herein relategenerally to methods and systems for operating acoustic imaging systems,such as those integrated into the electronic device(s) depicted in FIGS.1A-1C. Many acoustic imaging systems described herein can be generalizedto a simplified architecture including an acoustic medium (e.g., asubstrate; typically a monolithic substrate) with two parallel surfacessuch as a top surface and a bottom surface.

For convention herein, the bottom surface is understood to be coupled to(e.g., adhered to or otherwise in mechanical communication with) atleast a portion of the acoustic imaging system such that the acousticimaging system is acoustically/mechanically coupled to the acousticmedium via the bottom surface. Similarly, the top surface of an acousticmedium described herein is understood to define an imaging surface; anobject engaging the top/imaging surface may cause reflection(s) back tothe bottom surface that, in turn, can be used to generate an imageleveraging techniques described herein.

An array of acoustic transducers can be arranged in a pattern andpositioned near the bottom surface. As described above, to capture animage of an object engaging the top surface, an acoustic imaging systemcan cause the array, or only a portion thereof, to propagate an acousticpulse through the bottom surface of the acoustic medium and toward theobject.

When the acoustic pulse reaches the top surface of the acoustic medium,a portion of the acoustic pulse may be reflected back towards the arrayof acoustic transducers. As noted with respect to other embodimentsdescribed herein, the reflection(s) can be collected as an acousticoutput from the acoustic medium and an image of the top surface of theacoustic medium can be approximated. In many embodiments, theseoperations of driving at least a portion of the array and receivingvoltage signals (or current signals, or any other electrical signal)from the array (corresponding to reflections from the top surface of theacoustic medium, as referred to as the imaging surface), can beperformed at least in part by an application-specific integratedcircuit.

In many embodiments, an acoustic imaging system can implement the arrayof acoustic transducers as a number of individual ultrasonic elementsformed from piezoelectric material such as lead zircanate titinate, zincoxide, aluminum nitride, or any other piezoelectric material.

Piezoelectric materials may be selected for the speed with which thematerials can react to an electrical stimulus or excitation and/ormechanical stimulus or excitation. In other words, piezoelectricmaterials can be selected for certain acoustic imaging systems requiringacoustic pulses of particularly high frequency (e.g., megahertz scale,such as 50 MHz).

In these examples, to capture an image of an object engaging the topsurface (e.g., fingertip, stylus tip, and so on), the imaging system cancause one or more array of piezoelectric transducers to propagate anacoustic pulse (e.g., such as a plane wave or as a localized pulsehaving a specified center frequency) generally normal to the bottomsurface and toward the object in order to monitor for any acousticsignals reflected therefrom. As noted above, this operation is referredto herein as “driving” the array of piezoelectric transducers. In othercases, driving a piezoelectric transducer/element may not necessarilygenerate an acoustic pulse normal to the bottom surface.

For example, as may be appreciated, an acoustic pulse may propagate froma single point source along a generally spherical three-dimensionaltrajectory. In some examples, such as noted above, acoustic energypropagating along a particular angle from a point source (e.g., a singleacoustic transducer) may be timed so as to constructively interfere withan acoustic pulse output from a different acoustic transducer.

Such embodiments leverage beamforming techniques and/or phased arraycontrol techniques to increase signal-to-noise ratios and/or imagecontrast. It is appreciated that these examples are not exhaustive;other driving/timing/control means may be possible in view of thedescription provided herein. For simplicity of description, manyembodiments described herein reference a control schema in which anapplication-specific integrated circuit tasked with driving apiezoelectric transducer does so one transducer at a time. It isappreciated, however, that this is merely one example; in other cases,multiple transducers can be simultaneously driven and/or driven in aspecifically-timed sequence (e.g., for beamforming purposes).

Notwithstanding the foregoing, and as described in reference to otherembodiments described herein, when the acoustic pulse reaches theimaging surface of the acoustic medium, a portion of the acoustic pulsemay be reflected from the imaging surface and back towards the array ofpiezoelectric transducers as a result of the acoustic boundary (e.g.,acoustic impedance mismatch) between the imaging surface and the portionof object engaging it.

For example, a ridge of a fingerprint may present a different acousticboundary when touching the acoustic medium (e.g., soft tissue boundary)than a valley of a fingerprint (e.g., air boundary). Accordingly, aridge of a fingerprint may reflect the acoustic pulse differently than avalley of a fingerprint. In other words, a ridge of a fingerprintproduces a different acoustic output than a valley of a fingerprint.

When the acoustic pulse returns to the array of piezoelectrictransducers, the elements can be used to capture the reflection aselectrical signals or, more precisely, an application-specificintegrated circuit conductively coupled to one or more of thepiezoelectric transducers receiving the reflections may include ananalog to digital converter configured to sample (at aNyquist-appropriate frequency) voltage output from the one or more ofthe piezoelectric transducers. As noted above, this operation isreferred to herein as “sensing” or “imaging” with the array ofpiezoelectric transducers. In other cases, voltage sampling may not berequired; capacitive storage may be used (as one example) to determinevoltage output at a given time.

For example, when an array of piezoelectric transducers receives aportion of the acoustic reflection affected by a ridge of a fingerprint,that array of piezoelectric transducers may produce an electrical signalthat is different than the electrical signal produced by an array ofpiezoelectric transducers receiving a reflection affected by a valley ofa fingerprint.

By analyzing the electrical signals, the imaging system can derive animage of the object engaging the imaging surface of the acoustic medium.For example, each electrical signal can correspond to one pixel of theimage. In one embodiment, a pixel corresponding to an electrical signalaffected by a ridge of a fingerprint may be lighter than a pixelcorresponding to an electrical signal affected by a valley of afingerprint.

As may be appreciated, this may be due to the fact that the acousticimpedance mismatch between air and the acoustic medium is greater thanthe acoustic impedance mismatch between a fingerprint ridge and theacoustic medium.

FIG. 2A depicts a simplified block diagram of an acoustic imagingsystems that can be used with the electronic device 100 of FIG. 1 . Theacoustic imaging systems 200 can include one or more acoustictransducers 202. The acoustic transducers 202 can contract or expandrapidly in response to an electrical stimulus such as a voltage orcurrent (e.g., electroacoustic transducer). For example, the acoustictransducers 202 can be formed, in certain embodiments, from apiezoelectric material such as lead zircanate titinate, zinc oxide,aluminum nitride, or any other piezoelectric material and may have apiezoelectric response characterized as d31, d32, or d33.

In many embodiments, the acoustic transducers 202 can be configured forboth emitting and detecting acoustic signals. In other words, anacoustic transducer 212 can be used to both transmit an acoustic pulsein response to an electrical stimulus/excitation (such as from a voltagewavelet generated by an application-specific integrated circuit, such asdescribed herein) and, in addition, can generate a voltage signal inresponse to an acoustic output (e.g., acoustic/mechanical energyreceived as a reflection) from the acoustic medium.

In many examples, the acoustic transducers 202 can be arranged in apattern. For example, in some embodiments the acoustic transducers 202can be arranged in an evenly spaced line such as illustrated in FIG. 2A.In some embodiments, the acoustic transducers 202 can be arranged in amatrix or grid, as shown in FIG. 2B. In some examples, the matrix of theacoustic transducers 202 can be square or otherwise rectangular. Inother examples, the matrix of the acoustic transducers 202 can takeother shapes, such as a circular pattern (not shown).

Although many embodiments described herein distribute the acoustictransducers 202 in a uniform pattern (e.g., matrix, square, line,circle, and so on), such uniformity is not necessarily required, and insome examples, different regions may enjoy differentconcentrations/pitches of acoustic transducers.

The acoustic transducers 202 can be coupled to a controller 204, alsoreferred to as an application-specific integrated circuit. Thecontroller 204 can be configured to provide electrical energy (e.g.,voltage signals) to each acoustic transducer 212 independently, or togroups of acoustic transducers collectively/simultaneously. For example,the controller 204 can provide a first voltage signal (e.g., chirp,wavelet, and so on) to a first transducer and a second voltage to asecond transducer (e.g., phase-shifted chirp, wavelet, and so on). Inaddition, the controller 204 can control the duration and magnitude ofthe electrical energy applied to each independent acoustic transducer212. Further, the controller 204 can be configured to control a centerfrequency of any voltage signal applied to the transducers; for example,the controller 204 can be configured to control a center frequency of awavelet to be greater than 40 MHz, such as 50 MHz.

In many examples, the controller 204 can operate in one or more modes,either simultaneously, according to a duty cycle, or in another suitablemanner. In certain embodiments, the controller 204 can have anintegration mode.

In other embodiments or implementations, the integration mode can bereferred to as an integration mode or a drive mode. Accordingly, as usedherein, terms and phrases such as “integration mode” and “drive mode”,may be understood to each refer to the same operational mode of anacoustic imaging system.

When in the integration mode, the controller 204 can be configured toprovide electrical energy in the form of a voltage signal having highfrequency content (e.g., a center frequency above 40 MHz, such as 50MHz) to one or more of the acoustic transducers 202 and in response, theacoustic transducers 202 can produce an acoustic output, referred toherein as an acoustic pulse. As may be appreciated the acoustic pulseproduced by one or more transducers typically exhibits the samefrequency content as the voltage signal used to excite the transducers.

In many embodiments, and as noted above, the acoustic imaging system 200can be disposed within a housing of an electronic device.

In some examples, the acoustic imaging system 200 can be segmented intoan array of sub-portions. Each subportion may include a dedicatedcontroller 204, or at least a dedicated portion of the controller 204.For example, in some embodiments, the acoustic transducers 202 can bearranged in a high aspect ratio (e.g., greater than 1) array of 128×42.

In this configuration, the array can be subdivided into a grid of 4×2tiles, in which each subportion of the grid includes 32×21 individualacoustic transducers. Each of these individual subgroups of acoustictransducers can be controlled and/or operated independent of each of theother individual subgroups of acoustic transducers. In some examples,each individual subgroup (or “tile”) is associated with a respectivededicated controller 204 which can perform both drive and/or senseoperation for that individual tile.

In other cases, only a portion of the operations of a controller (e.g.,drive operations, sense operations, filtering operations, beamformingoperations and so on) can be dedicated to a particular tile. Forexample, in some cases, each tile may have a shared analog front end forsensing, may share a drive controller for drive operations, and so on.

In view of the foregoing, it may be appreciated that an array ofacoustic transducers as described herein can be subdivided into any setof tiles, which may be rectilinear, square, or may follow any pattern(e.g., tessellating pattern s, concentric patterns, linear patterns,rows and columns, and so on). Each subdivision of an array of acoustictransducers as described herein can be controlled independently withindependent control electronics, and/or may be controlled in cooperationwith one or more other subdivisions or tiles.

For example, FIG. 2C depicts the acoustic imaging system of FIG. 2Apositioned below an acoustic medium 206. As noted with respect to FIG. 1, the acoustic medium 206 can be a portion of a display, a portion of aninput device (e.g., button, switch, and so on), or a portion of thehousing of the electronic device. The acoustic medium 206 can includeactive components (e.g., circuits, circuit traces, batteries, and so on)or passive components (e.g., glass sheet, metal sheet, and so on) or acombination thereof.

The acoustic medium 206 defines a bottom surface and an imaging surface.The bottom surface is coupled to the acoustic transducers 202 via anadhesive layer 208, which may be optional. The imaging surface of theacoustic medium 206 is opposite the bottom surface and isconfigured/oriented to receive an object, such as a finger of a user210. As with other embodiments described herein, the finger of the user210 may include one or more features that introduce different acousticimpedance mismatches when wetting to the imaging surface of the acousticmedium 206.

The acoustic transducers 202 can be positioned below the acoustic medium206 so as to be in acoustic communication with the bottom surface,acoustically coupled to the bottom surface via the adhesive layer 208.In this manner, when an acoustic transducer 212 generates an acousticwave 214 in response to an excitation from the controller 204 (in theinterrogation mode), the acoustic wave 214 can propagate into theacoustic medium 206, through the bottom surface, toward the imagingsurface and, in turn, toward any feature(s) of the fingerprint of theuser 210, such as a valley 216 or a ridge 218.

While the acoustic wave 214 propagates through the acoustic medium 206toward the imaging surface, the controller 204 can transition partly orentirely into an imaging mode, such as depicted in FIG. 2D. When in theimaging mode, the controller 204 can be configured to receive, sample,and/or analyze an electrical signal from one or more of the acoustictransducers 202 that corresponds to an acoustic output of the acousticmedium 206 resulting from a portion of a reflection (such as reflections214 a, 214 b, or 214 c) of the acoustic wave 214 (see, e.g., FIG. 2C),such as may originate as a result of wetting of the ridge 218 to theimaging surface and/or as a result of an air gap captured by the valley216. It may be appreciated that a certain portion of energy of theacoustic wave 214 may be absorbed by the user's finger; this absorbedenergy is depicted as the acoustic wave 214 d.

Phrased in another non-limiting manner, in many embodiments, an acousticreflection from a particular location along the imaging surface maydepend upon whether that location is below the ridge 218 or the valley216. More particularly, the acoustic boundary between the acousticmedium 206 and the ridge 218 (having an acoustic impedance of softtissue) may cause a measurably smaller amplitude acoustic reflectionthan the acoustic boundary between the acoustic medium 206 and thevalley 216 (having an acoustic impedance of air).

As noted above, the amplitude of a reflection from a ridge/acousticmedium acoustic boundary may be a smaller than the amplitude of areflection from a valley/acoustic medium acoustic boundary. In otherwords, the amplitude of an acoustic reflection 216 c from an area of theimaging surface that is below a ridge 218 may be less than the amplitudeof an acoustic reflection 214 a, 214 b from an area of the imagingsurface that is below a valley 216. Accordingly, the controller 204,when in an imaging mode, can monitor the amplitude (and/or timing,phase, or any other suitable property) of an acoustic reflection toderive, determine, assemble, or create, an image of the ridges andvalleys of a user's fingerprint or, more generally, any suitable contourof any suitable object wetting to the imaging surface.

Accordingly, more generally and broadly, it may be appreciated that anacoustic imaging system such as described herein includes two primarycomponents: an array of acoustic transducers and an application-specificintegrated circuit configured to operate in a drive mode and a sensemode. In some examples, the drive mode and the sense mode can be timemultiplexed, whereas in other examples, a drive mode may be configuredto operate in one region while a sense mode is configured to operate inanother region.

A person of skill in the art may readily appreciate that any suitablecontrol schema can be used. For example, in some cases as describedherein beamforming techniques can be used to concentrate acoustic energyoutput from two or more acoustic transducers of an array of acoustictransducers at a particular location. In some examples, beamforming mayalso be used in a receive mode to spatially filter a received signal orset of received signals.

Further, it may be appreciated that a planar imaging surface is not arequirement of the embodiments described herein. A person of skill inthe art may readily appreciated that the systems methods andarchitectures described herein can be readily applied to image wettingof an object to a non-planar surface. For example, FIG. 2E depicts anacoustic imaging systems 200 can include one or more acoustictransducers 202 communicably coupled to a controller 204 that can beconfigured to operate in a drive mode and/or a sense mode, such asdescribed above.

The controller, as with other embodiments described herein can operatethe one or more acoustic transducers 202 as a monolithic entity (e.g.,driving all or substantially all transducers at the same time togenerate a plane wave) or may subdivide control of the array oftransducers such that only some of the one or more acoustic transducers202 are actively imaging (e.g., being driven and/or used for sensing) atany given time.

In such examples, it may be appreciated that the controller can executeany suitable sweep pattern, beamforming technique, or spatial ortemporal filtering technique. In this example, however, the acousticmedium 206 may take a nonplanar shape, such as a convex shape.

An example implementation in which the acoustic medium 206 has a convexshape may be an implementation in which the acoustic imaging system 200is incorporated into a sidewall of a housing of an electronic device,such as shown in FIGS. 1B and 1C. In other cases, the acoustic imagingsystem 200 can be incorporated into an electronic device that has acurved portion of a housing, such as a smartwatch with a curved exteriorsurface (which may be a sidewall surface, a crown surface, a buttonsurface, or any suitable exterior surface).

Further to the foregoing, it may be appreciated that convex and planarsensing plat shapes are not limiting; more generally, any acousticmedium geometry and/or acoustic medium side cross-section can be used.For example, FIG. 2F depicts a convex acoustic medium 206 that may beused in certain implementations.

It may be appreciated by a person of skill in the art that an acousticimaging system as described herein can be incorporated into any suitableelectronic device, whether portable or stationary, and may be positionedrelative to any suitable acoustic medium or sensing surface or imagingsurface. In some examples, the acoustic medium may be planar and formedfrom glass. In other cases, the acoustic medium may be nonplanar and maybe formed from metal, such as titanium.

In yet other examples, the acoustic medium may be curved and/orpatterned and the acoustic medium may be a ceramic material. It may befurther appreciated that control of an acoustic imaging system may varyby implementation in part due to differences in acoustic propagationspeed through different materials. In other words, it may be appreciatedthat an acoustic imaging system as described herein can be incorporatedin to many electronic devices, formed from many different materials, andmay necessarily operate and/or be configured to operate in differentmanners based on the selected implementation.

FIG. 3 depicts a simplified block diagram of an acoustic imaging system300 having both drive and sense modes of operation. An acoustictransducer array 302 can include two or more acoustic transducers. Forexample, in some embodiments the acoustic transducer array 302 caninclude an N×M array of individual transducers, which in turn can besubdivided and/or tiled into an A×B array of tiles, each tile including(N/A)×(M/B) individual acoustic elements. For example, an acoustic arraycan include 1000×100 acoustic elements, divided into 10×2 tiles. In thisexample, each tile includes 100×50 transducers. In this example, thearray is rectilinear and has a high aspect ratio (e.g., greater than2.0), but this structure may not be required of all embodiments.

Returning to FIG. 3 , conductively coupled to the acoustic transducerarray 302 can be a drive controller 304, which may be a portion of anapplication-specific integrated circuit, such as described herein. Thedriver controller 304 can be configured to deliver a voltage signal,such as a wavelet with a specified center frequency, to one or moretransducers of the acoustic transducer array 302.

In some cases, the drive controller 304 can be implemented as aplurality of drive controllers 304. For example, in such an embodiment,each individual transducer of the array of acoustic transducers 302 canbe coupled to a respective one drive controller 304. In another example,a single drive controller 304 can be coupled to a subset or subarray ofacoustic transducers of the array of acoustic transducers 302. In theseand related embodiments, adjacent transducers (and/or all transducers ofthe acoustic transducer array 302) can share one or more electrodes ortraces associated with the drive controller 304.

Conductively coupled to the acoustic transducer array 302 can be a sensecontroller 306, which may be a portion of an application-specificintegrated circuit, such as described herein. The sense controller 306can be configured to receive a voltage signal (or any other suitableelectrical signal) from one or more transducers of the acoustictransducer array 302. As with the drive controller 304, in some cases,the sense controller 306 can be implemented as a plurality of sensecontrollers 306.

For example, in such an embodiment, each individual transducer of thearray of acoustic transducers 302 can be coupled to a respective onesense controller 306. In another example, a single sense controller 306can be coupled to a subset or subarray of acoustic transducers of thearray of acoustic transducers 302. In these and related embodiments,adjacent transducers (and/or all transducers of the acoustic transducerarray 302) can share one or more electrodes or traces associated withthe sense controller 306.

These foregoing embodiments depicted in FIGS. 2A-3 and the variousalternatives thereof and variations thereto are presented, generally,for purposes of explanation, and to facilitate an understanding ofvarious configurations and constructions of a system, such as describedherein. However, it will be apparent to one skilled in the art that someof the specific details presented herein may not be required in order topractice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions ofspecific embodiments are presented for the limited purposes ofillustration and description. These descriptions are not targeted to beexhaustive or to limit the disclosure to the precise forms recitedherein. To the contrary, it will be apparent to one of ordinary skill inthe art that many modifications and variations are possible in view ofthe above teachings.

For example, acoustic transducers such as described herein can beconstructed in a number of ways. In typical embodiments, an acoustictransducer or, more precisely, an array of acoustic transducers, ismanufactured using thin-film deposition techniques such that the arrayis formed over and/or formed with an application-specific integratedcircuit that performs drive and sense operations, such as describedherein. However, this is merely one example construction; otherembodiments in which a stack of layers defining an acoustic transduceris disposed over an application-specific integrated circuit are alsopossible in view of the description provided herein.

For example, generally and broadly, FIGS. 4-5 depict simplified systemdiagrams of an acoustic imaging system, such as described herein, thatcan be formed entirely using a thin-film manufacturing process in whichan integrated circuit or any other suitable CMOS or other semiconductorcircuitry is formed in substantially the same process as an array ofthin-film, individually addressable piezoelectric transducers suitableto generate an acoustic pulse or a phased-array of acoustic pulses, suchas described herein.

As a result of these described and related configurations, an acousticimaging system such as described herein can be manufactured without arequirement for alignment of an array of microelectromechanicalpiezoelectric transducers with signal traces, solder pads, or otherelectrical or mechanical coupling(s), as noted above. As such, anacoustic imaging system, such as described herein, can be manufacturedat a more rapid and cost-effective pace and/or can be coupled to anacoustic medium (such as an electronic device housing as shown in FIGS.1A-1C) to define an imaging surface in a number of suitable ways,several of which are described below.

FIG. 4 depicts a simplified detail view of a thin-film acoustic imagingsystem, such as described herein (see, e.g., FIG. 1A, taken throughsection A-A), including a piezoelectric actuator formed from a thin filmthat exhibits a piezoelectric property or response, such aspolyvinylidene fluoride (PVDF) or trifluoroethylene (TrFE). In somecases, the thin film may be formed from a copolymer such as a vinylidenefluoride and trifluoroethylene blend (e.g., PVDF-TrFE). In some cases, amaterial such as PVDF-TrFE may be selected due at least in part tosimplicity of manufacturing and CMOS-compliant annealing temperatures.

In this embodiment, a high impedance stack of layers 400 is shown. Thehigh impedance stack of layers 400 defines a piezoelectric element thatis also referred to as an acoustic transducer. The transducer isconfigured to convert acoustic energy into electrical potential and viceversa.

In this example, the high impedance stack of layer 400 includes athin-film piezoelectric layer 402 that is configured to expand andcontract along a vertical axis. The thin-film piezoelectric layer 402may be monolithic or may be segmented and/or divided to define multiplediscrete acoustic transducers. For simplicity of illustration, only asingle acoustic transducer is shown in FIG. 4 , but it may beappreciated that the thin-film piezoelectric layer 402 may be used todefine multiple discrete acoustic transducer elements.

The thin-film piezoelectric layer 402 is supported by a support layer404 (which may also be referred to as an oxide layer, or any othernon-conductive insulating layer of material; the layer may be contiguousand/or monolithic or may be formed from multiple layers of material)that encloses a first electrode 406 (which is understood as a portion ofa first electrode layer, in array-based acoustic imaging systemembodiments; in such examples, the first electrode 406 is a member of anarray of electrodes, each of which is isolated from each other and/orconductively decoupled from one another to define an array ofelectrically distinct and individually-addressable electrodes) against abottom surface of the thin-film piezoelectric layer 402.

The support layer 404 can be made of a metalloid oxide, such as silicondioxide. In such embodiments, the support layer 404 may be referred toas a metalloid oxide layer, a passivation layer, an encapsulation layer,or a dielectric layer.

The first electrode 406 can be made from a metallic, and electricallyconductive, material such as aluminum. A second electrode 408 (which, aswith the first electrode layer is understood as a portion of a secondelectrode layer, in array-based acoustic imaging system embodiments; thelayer may be monolithic or segmented, as described above with respect tothe first electrode layer) is disposed onto a top surface of thethin-film piezoelectric layer 402, and may also be made from a metalmaterial, such as molybdenum. In other cases, other metal materials orelectrically conductive materials may be used.

The second electrode 408 may be coupled, via an optional adhesive/epoxylayer 410, to a lower surface of an acoustic medium 412. In other cases,the optional adhesive/epoxy layer 410 may be, or may include, apassivation material, such as SiO2.

As a result of this construction, a controller 414 (which may be aportion of an application-specific integrated circuit, such as describedherein) can be conductively coupled to the first electrode 406 and thesecond electrode 408 via one or more routing traces (such as the traces416, 418) so that the controller 414 can both drive the thin-filmpiezoelectric layer 402 and sense electrical signals from the thin-filmpiezoelectric layer 402.

More specifically, as a result of the depicted construction, a voltagesignal (such as a chirp signal or a wavelet) output from the controller414 can cause a voltage potential difference between the first electrode406 and the second electrode 408 (polarity and/or frequency content ofthe voltage may vary from embodiment to embodiment) thereby causing thethin-film piezoelectric layer 402 to vertically expand or contract inproportion to the voltage signal which, in turn, results in a mechanicaldeformation of the thin-film piezoelectric layer 402 along a directionperpendicular to a lateral axis, normal to the lower surface of theacoustic medium 412, thereby generating an acoustic pulse through theadhesive/epoxy layer 410 that can, thereafter, propagate into andthrough the acoustic medium 412.

Thereafter, reflections from an upper surface 414, some of which may beabsorbed as a function of acoustic impedance mismatch, may propagatethrough the acoustic medium 412 back to the thin-film piezoelectriclayer 402

In one specific implementation, the support layer 404 has a thickness ofapproximately 2 μm, the first electrode 518 has a thickness ofapproximately 0.1 μm, the thin-film piezoelectric layer 402 has athickness of approximately 1.0 μm, the second electrode 412 has athickness of approximately 0.1 μm, and the adhesive/epoxy layer 416 hasa thickness of approximately 3 μm.

These foregoing example thickness are merely illustrative of therelative thickness of the various layers that may be appropriate incertain configurations. In many examples, different thicknesses,including relative thicknesses may be suitable, especially uponconsideration of a center frequency output by and received by thecontroller 414.

As a result of these constructions, a stiffener layer and a backing(which may be a vacuum cavity or other sealed volume) typical ofconventional Piezoelectric Micromachined Ultrasonic Transducers(pMUT)/microelectromechanical transducers may be eliminated, along withmanufacturing complexities and costs associated therewith. In addition,due at least in part to the reduced relative thickness of theadhesive/epoxy layer, an improved acoustic coupling between the highimpedance stack of layers (such as shown in FIG. 4 ) and an acousticmedium can be achieved. This may be particularly advantageous forcoupling to certain materials such as metals or ceramics, which may beselected for electronic device housings.

As noted with respect to other embodiments described herein, each layerdepicted and described with reference to FIG. 4 can be manufacturedusing a thin-film deposition/manufacturing process. In such examples,alignment complexities and other manufacturing challenges related totolerances can be eliminated.

For example, as noted with respect to other embodiments describedherein, a high impedance stack of layers forming an acoustic transducer,such as described herein can be formed along with and/or over anapplication-specific integrated circuit that, in turn, can be configuredto perform, coordinate, trigger, or otherwise execute one or moreoperations of a controller such as described herein.

Examples include driving one or more transducers and/or sensing with oneor more transducers. For example, FIG. 5 depicts the stack-up as shownin FIG. 4 (the description of which is not repeated herein) formed atopa semiconductor circuit that defines one or more operations of thecontroller 414 (e.g., drive operations, sense operations, beamformingcontrol, and so on), which as noted above may be an application-specificintegrated circuit or any other suitable thin-film transistor circuit,pattern of electrical traces, bridges, or pads, or any other suitableanalog or digital circuitry.

For example, as with the embodiment depicted in FIG. 4 , the embodimentshown in FIG. 5 includes a thin-film piezoelectric layer 502 disposedover a dielectric layer 504 which encloses, against the thin-filmpiezoelectric layer 502, a first electrode 506. The embodiment 500 alsoincludes a second electrode 508 that in turn may be coupled via anadhesive 510 to an acoustic medium 512. Each of these layers may beformed over an integrated circuit 514.

In this example, the integrated circuit 514 may be formed by leveragingone or more conventional semiconductor manufacturing techniques suitablefor forming one or more switching circuit elements and/or electricaltraces. Example processes that may be used include lithographicprocesses, etch processes, implantation processes, mechanical and/orchemical polishing processes, annealing processes, and so on. A personof skill in the art appreciates that any suitable process or processsequence can be used to form any suitable circuit, the design andimplementation of which varies from embodiment to embodiment.

Once the integrated circuit 514 is formed, the dielectric layer 504 canbe disposed thereover using a suitable deposition or growth methodology.Next, a layer of conductive material can be disposed onto the newlydeposited dielectric layer. This layer can be masked and etched todefine geometry and positioning of the first electrode 506. Next,optionally, additional dielectric can be disposed to fullyenclose/encapsulate the newly-defined first electrode. In other cases,the dielectric layer can be etched and filled with a material suitablefor the first electrode. A person of skill in the art appreciates thatmay options are possible.

Over the first electrode and dielectric the thin-film piezoelectriclayer 502 can be formed using a suitable technique (e.g., spindeposition). Optionally one or more of these layers can be mechanicallyor chemically polished or treated and/or otherwise prepared betweendevelopment of subsequent layers. Over the thin-film piezoelectric layer502, the second electrode layer can be formed. In some cases,intervening mask/etch processes may be required or preferred to developparticular geometry and/or structural features.

The foregoing example manufacturing method is not exhaustive of allmethods that may be leveraged to form a thin-film piezoelectric layersuch as described herein. Generally and broadly, it may be appreciatedthat because theses acoustic transducers can be formed with conventionalsemiconductor manufacturing methodologies, any suitable number ofacoustic transducers can be formed over any suitable CMOS or othersemiconductor circuitry, such as circuitry required to operate anacoustic transducer as described herein (e.g., drive mode, sense mode,and so on).

In addition, it may be appreciated that these foregoing exampleembodiments are not exhaustive of the various constructions of anacoustic imaging system, such as described herein. For example, althougha single acoustic element (e.g., piezoelectric element) is depicted inFIGS. 4-5 , it may be appreciated that an acoustic imaging system suchas described herein it typically implemented with multiple discreteand/or physically-separated acoustic transducers arranged in atwo-dimensional array (which may be flat and/or may follow a particularcurve contouring to a particular acoustic medium geometry), each ofwhich may be conductively coupled to at least a portion of anapplication-specific integrated circuit configured to initiate driveoperations and/or sense operations leveraging said acoustic transducers.In particular, in such embodiments, the array of acoustic transducersmay each include two discrete electrodes (e.g., an electrode pair) thatcan be individually conductively coupled to an application-specificintegrated circuit, some or all of which may be physically coupled tothe transducer itself, such as shown in FIG. 5 .

In such embodiments, an array of electrode pairs, each of which isassociated with a discrete piezoelectric actuator/acoustic transducer,can be disposed in a grid or matrix pattern, such as described above. Inmany cases, each electrode of an electrode pair takes the same shape andsize, but this is not required; some embodiments include an upperelectrode coupled to a top surface of a piezoelectric actuator that ismade from a different material, in a different shape, formed to adifferent thickness, and so on contrasted with a lower electrode coupledto a bottom surface of the same piezoelectric actuator.

More generally and broadly, it may be appreciated that layers describedabove may be formed form a number of different materials, and/or may beformed in a number of suitable processes. For example, in some cases oneor more electrodes of can be aluminum which may be sputtered to athickness of 100 nm, or a greater thickness or a smaller thickness. Insome cases, an adhesion layer may be formed as well to promoteelectrical and mechanical coupling. Titanium is one example materialthat may be used as an adhesion layer.

In other cases, other metals may be used for electrodes. In someexamples, one electrode may be made from a first material to a firstthickness (e.g., Al to 100 nm), and a second electrode can be made froma second material to a second thickness (e.g., Al/Ti to 100 nm);embodiments and implementations vary.

In some cases, a PVDF-TrFE thin-film layer can be formed by depositing apowder/solvent solution, allowing the solvent to evaporate, andthereafter annealing. In such examples, a PVDF-TrFE layer may be formedto a thickness of approximately 1.5 μm, or less than or greater than thesame. Such a layer may be etched into multiple discrete regions by asuitable mechanical, chemical, electrical or other etching process suchas reactive ion etching process.

These foregoing embodiments depicted in FIGS. 4-5 and the variousalternatives thereof and variations thereto are presented, generally,for purposes of explanation, and to facilitate an understanding ofvarious configurations and constructions of a single transducer of anacoustic imaging system, such as described herein. However, it will beapparent to one skilled in the art that some of the specific detailspresented herein may not be required in order to practice a particulardescribed embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions ofspecific embodiments are presented for the limited purposes ofillustration and description. These descriptions are not targeted to beexhaustive or to limit the disclosure to the precise forms recitedherein. To the contrary, it will be apparent to one of ordinary skill inthe art that many modifications and variations are possible in view ofthe above teachings.

For example, as noted above, in many examples an acoustic imaging systemas described herein can include an array of acoustic transducers. Thearray of acoustic transducers can be formed such as described above. Forexample, the array of transducers can be defined by a number ofindividual acoustic transducers, each of which is defined by a portionof a thin-film piezoelectric material disposed between two electrodesdedicated to that particular acoustic transducer.

In some examples, as noted above, the array of transducers can besubdivided and/or segmented into tiles. Each tile can included dedicatedelectronics optimized to drive and/or sense via the acoustic transducersof that particular tile. Such constructions and configurations candramatically improve signal to noise ratios, reduce cost, reduce powerconsumption, and reduce manufacturing and signal routing complexity.FIGS. 6A-6C are provided to illustrate an example construction in whicha high aspect ratio (e.g., 2) array of acoustic transducers, formed in athin-film process such as described above, are segmented.

In particular, FIG. 6A depicts a system diagram of a segmented acousticimaging system, as described herein. In this example, an array of thinfilm acoustic transducers 600 can include 336 individual transducers,arrange in a rectilinear pattern of 24×14. In this example, eighttiles/segments are shown, arranged in two rows of four tiles. Each tileincludes and is dedicated to 6×7 acoustic transducers of the 336transducers depicted in the illustrated embodiment.

In particular, a first tile 602 can include 42 separate and individuallyaddressable thin-film acoustic transducer, one of which is identified asthe acoustic transducer 604. Each transducer of the first tile 602,including the acoustic transducer 604 can be conductively coupled to adedicated analog front end via a signal bus 606. The dedicated analogfront end is identified in the figure as the tile front end 608.

In this construction, the tile front end 608 can be configured toreceive and process and/or condition one or more analog voltage signalsfrom one or more of the 42 acoustic transducers defining the first tile602. For example, the tile front end 608 can be configured to demodulateAC signals received from the acoustic transducer 604, filter a voltagesignal received from the acoustic transducer 604 (e.g., frequency-domainor time-domain filters, such as band pass, low pass, high pass, movingaverage, and so on), amplify a voltage signal received from the acoustictransducer, attenuate all or some of a voltage signal received from theacoustic transducer, store acoustic energy generated by the voltagesignal, integrate a time-varying voltage signal received from theacoustic transducer 604 over a given time window, offset and/or bias avoltage signal received from the acoustic transducer 604 by a givenamount or calibration value, and so on.

Other tiles of the array of thin film acoustic transducers 600 can beidentical to the first tile 602, such as described above. For example, asecond tile 610 can also include 42 independently addressable acoustictransducers, one of which is identified as the acoustic transducer 612.These transducers can be coupled to a tile front end 614. In the samemanner, other tiles can be coupled each to a respective tile front end.For example, the tile 616 can be coupled to the tile front end 618, thetile 620 can be coupled to the tile front end 622, the tile 624 can becoupled to the tile front end 626, the tile 628 can be coupled to thetile front end 630, the tile 632 can be coupled to the tile front end634, and the tile 636 can be coupled to the tile front end 638.

It may be appreciated that this example construction is merely providedas one example; any suitable number or arrangement of tiles may beselected. Similarly, in some embodiments, tiles may include differentnumbers of acoustic transducers. In other cases, some tiles may bedifferently shaped than other tiles. In some cases, tiles may beenclosed within other tiles (e.g., concentric arrangements). In othercases, one tile may circumscribe another tile. In some cases, some tilesmay be coupled to the at least one common transducer; in other words,some tiles may overlap such that different tile front ends may beconfigured to control the same acoustic transducers (e.g., forredundancy).

Similarly, it may be appreciated that each individual analog front endmay be configured in the same manner, or may be configured intile-specific ways. For simplicity of description, the embodiments thatfollow presume a construction in which each tile of a given embodimenthas the same number of transducers and is configured to operate inidentical ways. In such examples, each respective analog front end maybe defined, at least in part, in an integrated circuit over which theacoustic transducers of that particular tile are formed, such asdescribed above.

FIG. 6B depicts a schematic/signal flow diagram of an analog front endof a tile of a segmented acoustic imaging system as described herein.More specifically, the depicted analog front end may be the tile frontend 608 of the FIG. 6A, or any of the depicted tile front ends shown inFIG. 6A.

In particular, the tile front end 608 receives one or more input voltagesignals via the signal bus 606. The signal bus 606 can provide input toa multiplexer 640 configured to iteratively switch between individualtraces of the signal bus 606 so that individual signals corresponding tooutputs of individual acoustic transducers can be individually processedand/or conditioned.

The multiplexer 640 may be configured to provide as output a timemultiplexed voltage signal that iteratively shifts between two or moretransducers of the first tile 602. In some examples, the multiplexer 640is configured to linearly shift between transducers, advancing row byrow or column by column. In other cases, the multiplexer 640 isconfigured to follow a serpentine multiplexing pattern. In yet othercases, the multiplexer 640 can be controlled at least in part by abeamforming controller informing selection among traces associated withthe signal bus 606 based on a timing and/or phase difference pattern;any suitable pattern may be used, some of which may switch between allacoustic transducers, some of which may switch between only a subset ofthe acoustic transducers of the first tile 602.

At a given time, an output of the multiplexer 640 may correspond to asingle voltage signal generated by a single acoustic transducer. Forsimplicity of description the embodiments that follow reference anoutput of the acoustic transducer 604 as shown in FIG. 6A and describedin reference thereto. It may be appreciated however, that theembodiments and signal conditioning and modification operations andstages that follow may be likewise applied to any output of any suitableacoustic transducer or combination of transducers; in some examples,outputs from one or more transducers may be combined in the analogdomain prior to being received by the tile front end 608.

A voltage signal output from the multiplexer 640 is provided as input toa first amplifier 642, which may be configured to amplify the voltagesignal by a fixed or variable amount. A gain profile of the firstamplifier 642 may be linear or non-linear. In some cases, gain may befrequency dependent. In other cases, gain may be informed by and/orbased on a configuration parameter based on and/or associated withparticular individual acoustic transducers. In these embodiments,manufacturing differences between individual transducers can becompensated for by varying gain of the first amplifier 642. The gainprofile of the first amplifier 642 may be selected so as to not saturatedownstream signal processing electronics; in some cases, maximum gainmay be selected automatically as a result of feedback received from oneor more downstream signal processing stages. For example, a subsequentstage may be configured to detect when that stage is saturated orotherwise operating outside of a given operational parameter. In suchexamples, the subsequent stage may provider operational input to thefirst amplifier 642 to cause the first amplifier 642 to reduce its gain,at least with respect to a particular acoustic transducer.

An amplified voltage signal is output from the first amplifier 642 andprovided as input to a band pass filter 644. The band pass filter 644may be configured to attenuate and/or eliminate both high frequencycontent and low frequency content from the amplified voltage signal. Theband width and center frequency at which the band pass filter 644operates may vary from embodiment to embodiment.

In many cases, as noted above, an acoustic imaging system as describedherein can be configured to operate in a drive mode at a particularcenter frequency. For example, a pulse or input provided to a givenacoustic transducer may have a center frequency at a selected andcontrolled value. For convenient reference, this frequency is referredto herein as the “drive frequency,” the “drive center frequency,” ormore generally, the “carrier frequency.”

In these examples, the band pass filter 644 may be configured to filterthe amplified voltage signal around the carrier frequency at which theacoustic imaging system operates. For example, if the acoustic imagingsystem is configured to operate at 10 MHz, the center frequency of theband pass filter 644 may be selected to be 10 MHz, with a bandwidth of0.5 MHz. In other cases, other band widths and/or other centerfrequencies may be selected. For example, in some embodiments, a bandpass filter such as the band pass filter 644 may be configured to targeta harmonic of the carrier frequency. In other cases, the band passfilter 644 may have a larger band width; may configurations arepossible, many of which are implementation specific.

The band pass filter 644 is configured to output a passband signal. Thepassband signal can be provided as input to a high-frequency rectifier646. The rectifier 646 can be configured to be an asynchronousfull-bridge rectifier or a synchronous rectifier. In manyimplementations, the rectifier 646 is an active, synchronous rectifierso as to reduce conduction losses and forward bias voltage drop.

The rectifier 646 may be configured to output a rippled direct currentsignal. In some cases, the rippled direct current signal may be appliedas input to an optional low pass filter (e.g., a capacitor coupling therippled direct current signal to ground) or other envelope followingcircuit, such as the optional envelope follower 648.

The envelope follower 648 and/or any other envelope detection circuitrycan provide a low-frequency output voltage signal as input to anintegrator 650 configured to integrate the low-frequency output voltagesignal over a particular time window, which may be varied or constant.As a result of this construction the integrator 650 can effectivelyprovide an output voltage that corresponds, at least in part, to aquantity of acoustic energy lost during a preceding drive operation toan acoustic impedance mismatch at an imaging area/surface such asdescribed above.

More particularly, the greater an acoustic impedance mismatch betweenthe acoustic medium into which an acoustic pulse is generate (by theacoustic imaging system), the greater quantity of acoustic energy thatshould be received as a reflection at one or more of the acoustictransducers of the array of acoustic transducers. As one specificexample, a fingerprint valley accounts for a greater acoustic impedancemismatch than a fingerprint ridge, and is thus associated with a higheramplitude of acoustic reflection. As a result, an output of theintegrator 650 is expected to be greater in the presence of afingerprint valley than a fingerprint ridge.

As may be appreciated by a person of skill in the art, differentacoustic impedance mismatches may result in different quantities ofacoustic energy being received as a reflection at the acoustic imagingsystem. In particular, it may be the case—especially for particularacoustic media such as metals—that the overwhelming majority of acousticenergy received is from the drive signal itself. In another non-limitingphrasing, carrier noise dominates the signal received at the integrator650.

To account for carrier noise, many embodiments include an offset digitalto analog converter 652 configured to provide a fixed or variablevoltage output as input to the integrator 650 so that carrier amplitudeand/or carrier noise can be subtracted in real time from the output ofthe integrator 650. The offset digital to analog converter 652 can beconfigured to receive a digital control signal via a tap 654.

The tap 654 can provide a fixed voltage or a variable digital voltagebased at least in part on a drive signal applied to one or more acoustictransducers. The tape 654 can provide a digital bias value that isbased, at least in part, on feedback from an upstream or downstreamsignal conditioning stage. It may be appreciated by a person of skill inthe art that the offset digital to analog converter 652 can provide anysuitable offset that may vary based on beamforming operations, aposition or physical location of a particular acoustic transducer, awaveform selected to drive at least one acoustic transducer, a type orcharacteristic of an acoustic medium and so on.

As a result of this construction, the integrator 650 can be configuredto provide a conditioned signal via an output 656.

As noted above, each tile can be configured to operate in the samemanner as the first tile 608.

These foregoing embodiments depicted in FIGS. 6A-6B and the variousalternatives thereof and variations thereto are presented, generally,for purposes of explanation, and to facilitate an understanding ofvarious configurations and constructions of a segmented/tiled acousticimaging system with a hierarchy or staged arrangement of signalconditioning, such as described herein. However, it will be apparent toone skilled in the art that some of the specific details presentedherein may not be required in order to practice a particular describedembodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions ofspecific embodiments are presented for the limited purposes ofillustration and description. These descriptions are not targeted to beexhaustive or to limit the disclosure to the precise forms recitedherein. To the contrary, it will be apparent to one of ordinary skill inthe art that many modifications and variations are possible in view ofthe above teachings.

For example, as noted above, an output of an individual tile can beprovided as input to a single shared signal conditioning/analog todigital converter stage. FIG. 7 depicts a system diagram of a segmentedacoustic imaging system, as described herein.

As with other embodiments described herein, the acoustic imaging system700 includes a drive controller 702 that provides drive signals (whichmay have particular phase and/or waveform characteristics, following abeamforming pattern or scan plan) to one or more tiles and/or one ormore individual acoustic transducers of an array of thin-film acoustictransducers 704. As noted above, the array of thin-film acoustictransducers 704 may be segmented into tiles, each of which may beassociated with a dedicated one analog front end; collectivelytile-level analog front ends are illustrated as the front ends 706.

Output from the front ends 706 can be provided as input to single sharedanalog to digital converter stage 708 which can be tasked with, andconfigured to, provide a digital output value that corresponds toacoustic impedance mismatch at a particular location of an imagingsurface or imaging area associated with the acoustic imaging system 700.

More particularly, as noted above with respect to FIGS. 2A-2C, the drivecontroller 702 can include an oscillator 710 configured to provide astable high frequency signal that may be sampled to generate one or moredrive signals that, in turn, can be applied as input to one or moreacoustic transducers of the array of thin-film acoustic transducers 704.

In many examples, the oscillator 710 is configured to oscillate at astable frequency in the tens of MHz (e.g., 10 MHz, 20 MHz, 50 MHz, andso on), but this is not a requirement and a person of skill in the artmay readily appreciate that different—either higher or lower—frequenciesmay be appropriate in particular embodiments.

The oscillator 710 can be kept in phase relative to other signal linesof the system by a phase lock loop 712. In many examples, the phase lockloop 712 is configured to synchronize the oscillator 710—or an outputthereof—with a system clock and/or a harmonic thereof. As a result ofthis construction, downstream electronics, especially digitalelectronics, can be synchronized in with high frequency signals used inthe analog domain to generate drive signals such as described above.

An output of the phase lock loop 712 can be provided as input to a phasegenerator 714 which can be configured to provide outputs via a signalbus 716, each of which represent adifferently-delayed/differently-phased signal output from the phase lockloop 712. For example, in some embodiments the phase generator may beconfigured to provide eight signals as output; a first signal linetransits a voltage signal precisely in phase with output of the phaselock loop, a second signal line transits a voltage signal 22.5 degreesout of phase with the output of the phase lock loop 712, a third signalline transits a voltage signal 45 degrees out of phase with the outputof the phase lock loop 712, and so on.

Signals carried by the signal bus 716 can be provided as input to amultiplexer 718 that can be driven by a beamforming controller/scanplanner 720. The beamforming controller/scan planner 720 can beconfigured to select which signal line (i.e., which phase delay) toapply at a particular moment. As may be appreciated by a person of skillin the art, the beamforming controller/scan planner 720 can leverageone, and/or be leveraged by, or more beamforming controllers thatoperate by applying differently-phased signals to differently locatedacoustic transducers.

An output of the multiplexer 718, selected by the beamformingcontroller/scan planner 720, can be provided as input to an addressselector 722 configured to provide the output to a particular selectedacoustic transducer of the array of thin-film acoustic transducers 704via an output signal line 722. The address selector 722 can beconfigured to cooperate with the beamforming controller/scan planner 720or may operate independently; many configurations and control paradigmsare possible.

The signal carried by the output signal line 722 can be received at theintended, addressed, acoustic transducer of the array of thin-filmacoustic transducers 704, which may be a member of a first tile 724, asecond tile 726, or any other suitable tile. For simplicity ofillustration, a single acoustic transducer of the first title 724 isidentified as the target acoustic transducer 728.

As a result of this construction, when the target acoustic transducer728 receives the signal carried by the output signal line 722, thetarget acoustic transducer 728 generates a mechanical output into anacoustic medium that has a center frequency based at least in part onthe operating frequency (or a harmonic or sampled multiple thereof) ofthe oscillator 710.

As described with respect to other embodiments described herein, after adrive operation has been triggered, a sense operation may be initiatedin which one or more voltage signals generated by one or more acoustictransducers of the array of thin-film acoustic transducers 704 (whichmay include the target acoustic transducer 728) can be received via, forexample, a signal bus 730, at a tile-specific front end such as the tilefront end 732. The tile front end 732 can operate in much the samemanner as described above in reference to FIG. 6B; this description isnot repeated.

The tile front end 732—and/or other tile front ends—can provide outputthereof to a multiplexer 734 of the single shared analog to digitalconverter stage 708. The single shared analog to digital converter stage708 can provide output to another amplifier, identified as thepost-integration amplifier 736. As with other amplifiers describedherein, the post-integration amplifier 736 can be configured to operateaccording to any suitable variable or fixed gain profile.

The single shared analog to digital converter stage 708 also includes ahigh frequency and high fidelity analog to digital converter 738. Insome embodiments, a successive approximation analog to digital convertercan be used; although this is not required of all embodiments.

The high frequency and high fidelity analog to digital converter 738 canprovide a digital output to subsequent digital-domain processingsystems, such as a digital image processor 740, an image processor 742and/or a data store or key storage controller configured to gateoutput(s) of the acoustic imaging system 700 based on key-basedauthentication.

These foregoing embodiments depicted in FIG. 7 and the variousalternatives thereof and variations thereto are presented, generally,for purposes of explanation, and to facilitate an understanding ofvarious configurations and constructions of an acoustic imaging system,such as described herein. However, it will be apparent to one skilled inthe art that some of the specific details presented herein may not berequired in order to practice a particular described embodiment, or anequivalent thereof.

Thus, it is understood that the foregoing and following descriptions ofspecific embodiments are presented for the limited purposes ofillustration and description. These descriptions are not targeted to beexhaustive or to limit the disclosure to the precise forms recitedherein. To the contrary, it will be apparent to one of ordinary skill inthe art that many modifications and variations are possible in view ofthe above teachings.

For example, although signal lines in FIG. 7 and FIGS. 6A-6B areillustrated as single signal lines, in many embodiments, multiple linesmay be leveraged to convey differential signals.

In other examples, the acoustic imaging system 700 can be furtherconfigured for dark pixel subtraction. In such cases, a test controller746 may be configured to provide a test signal to drive one or moreacoustic transducers at a particular selected moment at which no imaginginput is expected. Thereafter, output from the analog to digitalconverter 738 and/or another signal processing or signal conditioningstage can be used and/or stored to be subtracted at a later time duringan imaging or sensing operation.

In yet other examples, additional carrier rejection operations can beperformed in addition to the carrier subtraction/offset digital toanalog converter described above in reference to FIGS. 6A-6B. Forexample, in some embodiments I-Q demodulation may be leveraged tomitigate effects of carrier noise. In other cases, envelope detectionand/or following may be employed. In yet further examples, devicespecific and/or pixel specific configuration or calibration parameterscan inform operations of the acoustic imaging system 700; some acoustictransducers and/or tiles may be associated with higher or lower gainthan other acoustic transducers or tiles. Such example embodiments canbe described as region-specific gain control embodiments.

In yet other examples, beamforming may be used for mechanical/analogcarrier noise rejection. As noted above, beamforming operations and scanplans can be implemented in a number of ways. In addition, it may beappreciated that different beamforming techniques may be suitable fordifferent implementations and/or different imaging conditions. Forexample, some scan plans may be more suitable in high humidityenvironments whereas other scan plans and/or beamforming techniques maybe more suitable for low humidity, high temperature environments. Insome examples, a first beamforming operation can be selected for a firstscan plan whereas a second beamforming operation is selected for asecond scan plan. In this example, the first scan plan can be performedprior to the second scan plan, after which results from both scan planscan be merged in a suitable manner.

Generally and broadly, FIGS. 8A-11C are provided to show various examplebeamforming operations associated with different scan plans or scanoperations. It may be appreciated that these examples are notexhaustive.

In particular, FIGS. 8A-8C depict a simplified cross-section of anacoustic imaging system as described herein, implementing a linear scandrive operation that leverages beamforming to focus acoustic energyemitted from multiple acoustic transducers at a selected location of acurved imaging surface.

In the illustrated embodiment, an acoustic imaging system 800 is shown.The acoustic imaging system 800 includes an application-specificintegrated circuit 802 that may be communicably, conductively, and/ormechanically coupled to an array of acoustic transducers 804. As withother embodiments describe herein, the application-specific integratedcircuit 802 of the acoustic imaging system 800 can be configured toperform or coordinate one or more drive or sense operations of theacoustic imaging system 800. Specifically, the application-specificintegrated circuit 802 may be configured to operate one or more acoustictransducers of the array of acoustic transducers 804 in a drive mode ora sense mode.

Further, the application-specific integrated circuit 802 can beconfigured to operate one or more acoustic transducers of the array ofacoustic transducers 804 according to a particular scan plan and/orbeamforming operation. In these embodiments, the application-specificintegrated circuit 802 can be configured as described above in referenceto FIG. 6A-7 , and may be configured to receive as input (and/or obtainfrom a database) one or more delay coefficients that theapplication-specific integrated circuit 802 can use to inform how andwhen drive signals are applied to one or more acoustic transducers ofthe array of acoustic transducers 804. For example, in a simplifiedembodiment, the array of acoustic transducers 804 can be configured toselect a subset of transducers from the array of acoustic transducers804 to operate in the drive mode. For convention, these selectedtransducers can be referred to as drive-mode transducers. A firstdrive-mode transducer can be drive by the application-specificintegrated circuit 802 with a time/phase delay of N, whereas a seconddrive-mode transducer can be driven by the application-specificintegrated circuit 802 with a time/phase delay of N+1, whereas a thirddrive mode transducer can be driven by the application-specificintegrated circuit 802 with a time/phase delay of N+2 and so on. It maybe appreciated that the application-specific integrated circuit 802 canapply any suitable delay to any suitable drive signal applied to anydrive mode transducers of the set of drive-mode transducers selectedform the array of acoustic transducers 804.

The acoustic imaging system 800 also includes an adhesive layer 806 thatacoustically and mechanically couples the array of acoustic transducers804 to a first surface of an acoustic medium 806 a, which has a curvedprofile. A curved profile is not required of all embodiments; someexamples include acoustic media of different cross-sectional profiles.

As a result of this construction, as with other embodiments describedherein, once the application-specific integrated circuit 802 applies anappropriate voltage signal to a given acoustic transducer of the arrayof acoustic transducers 804, that given acoustic transducer generates acorresponding mechanical wave that can propagate through the adhesivelayer 806 into the acoustic medium 806 a, traversing a thickness of theacoustic medium 806 a until that mechanical wave reaches a surface ofthe acoustic medium 806 a that is generally opposite the first surfaceof the acoustic medium 806 a, after which at least a portion of theenergy of the mechanical wave is reflected from that second surface (theimaging surface). The reflected wave traverses the acoustic medium 806 aagain and may be received at least one sense-mode transducer.

As noted above, the depicted embodiment illustrates a linear scan driveoperation that leverages beamforming to focus acoustic energy emittedfrom multiple acoustic transducers at a selected location of a curvedimaging surface. More particularly, the application-specific integratedcircuit 802 can be configured to select a scan plan that linearlyadvances from one fractional area of the imaging surface to anotherfractional area of the imaging surface. In this manner, theapplication-specific integrated circuit 802 rasterizes an image of anobject engaging the imaging surface, such as a fingerprint of a user808.

More specifically, in these examples, the application-specificintegrated circuit 802 can be configured to (1) select a fractional area810 a of the imaging surface, (2) select a scan plan and/or beamformingoperation that targets the fractional area 810 a, and (3) execute thatscan plan, such as shown in FIGS. 8A-8C.

In particular, as shown in FIG. 8A, a set of drive mode transducers anda set of sense mode transducers are selected from the array of acoustictransducers 804. In this embodiment, drive-mode transducers bookend(and/or circumscribe in a two-dimensional drive embodiment) thesense-mode transducers, but this is not required of all embodiments. Forreference and example, a sense mode transducer 812 a is identified andbookended by drive-mode transducers 814 a and 816 a. Although only asingle sense mode transducer is labeled, it may be appreciated that morethan one transducer can be operated in a sense mode. Similarly, althoughonly two drive-mode transducers are labeled, it may be appreciated thatmore than two transducers can be operated in a drive mode.

FIG. 8A depicts the drive-mode transducers 814 a and 816 a emittingacoustic energy (alongside, and timed with respect to adjacent and/orother drive-mode transducers) with specific timing such that a signalemitted from the drive-mode transducer 814 a arrives at the selectedfractional area of the imaging surface, the fractional area 810 a, atthe same time that a signal emitted from the drive-mode transducer 816 aarrives. As a result of this construction, reflections from these twosignals may constructively interfere toward the direction of thesense-mode transducer 812 a, thereby increasing a signal-to-noise ratioassociated with operated and/or receiving signals from the sense-modetransducer 812 a.

FIG. 8B depicts the scan plan of FIG. 8A advanced by a step. Inparticular, FIG. 8B depicts the drive-mode transducers 814 b and 816 bemitting acoustic energy (alongside, and timed with respect to adjacentand/or other drive-mode transducers) with specific timing such that asignal emitted from the drive-mode transducer 814 b arrives at adifferent selected fractional area of the imaging surface, thefractional area 810 b, at the same time that a signal emitted from thedrive-mode transducer 816 b arrives. As described above in reference toFIG. 8A, as a result of this construction, reflections from these twosignals may constructively interfere toward the direction of asense-mode transducer 812 b, thereby increasing a signal-to-noise ratioassociated with operated and/or receiving signals from the sense-modetransducer 812 b. In this example, timings associated with drivingand/or sensing by the application-specific integrated circuit 802 may bevaried with respect to the operation shown in FIG. 8A due to curvatureof the acoustic medium 806 a.

FIG. 8C depicts the scan plan of FIGS. 8A-8B advanced by another step.In particular, FIG. 8C depicts the drive-mode transducers 814 c and 816c emitting acoustic energy (alongside, and timed with respect toadjacent and/or other drive-mode transducers) with specific timing suchthat a signal emitted from the drive-mode transducer 814 c arrives at adifferent selected fractional area of the imaging surface, thefractional area 810 c, at the same time that a signal emitted from thedrive-mode transducer 816 b arrives. As described above in reference toFIGS. 8A-8B, as a result of this construction, reflections from thesetwo signals may constructively interfere toward the direction of asense-mode transducer 812 c, thereby increasing a signal-to-noise ratioassociated with operated and/or receiving signals from the sense-modetransducer 812 c. In this example, timings associated with drivingand/or sensing by the application-specific integrated circuit 802 may bevaried with respect to the operation shown in FIG. 8A due to curvatureof the acoustic medium 806 a.

The foregoing embodiments depicted in FIGS. 8A-8C and the variousalternatives thereof and variations thereto are presented, generally,for purposes of explanation, and to facilitate an understanding ofvarious operations of an acoustic imaging system, such as describedherein. However, it will be apparent to one skilled in the art that someof the specific details presented herein may not be required in order topractice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions ofspecific embodiments are presented for the limited purposes ofillustration and description. These descriptions are not targeted to beexhaustive or to limit the disclosure to the precise forms recitedherein. To the contrary, it will be apparent to one of ordinary skill inthe art that many modifications and variations are possible in view ofthe above teachings.

For example, a linear scan plan that follows a contour of an acousticmedium may not be suitable or preferred in all embodiments. For example,FIGS. 9A-9B depict a simplified cross-section of an acoustic imagingsystem as described herein, implementing a depth-averaging scan driveoperation that leverages beamforming to focus acoustic energy emittedfrom multiple acoustic transducers at a selected location to a selecteddepth, of a curved imaging surface.

As with the embodiment shown in FIG. 8A, in the illustrated embodiment,an acoustic imaging system 900 is shown. The acoustic imaging system 900includes an application-specific integrated circuit 902 that may becommunicably, conductively, and/or mechanically coupled to an array ofacoustic transducers 904. As with other embodiments describe herein, theapplication-specific integrated circuit 902 of the acoustic imagingsystem 900 can be configured to perform or coordinate one or more driveor sense operations of the acoustic imaging system 900. Theapplication-specific integrated circuit 902 may be configured in asimilar or identical manner to the application-specific integratedcircuit 802 shown in FIG. 8A; this description is not repeated.

As with other embodiments, the acoustic imaging system 900 canoptionally include an adhesive layer 906 that acoustically andmechanically couples the array of acoustic transducers 904 to a firstsurface of an acoustic medium 906 a, which has a curved profile. Acurved profile is not required of all embodiments; some examples includeacoustic media of different cross-sectional profiles.

As a result of this construction, as with other embodiments describedherein, once the application-specific integrated circuit 902 applies anappropriate voltage signal to a given acoustic transducer of the arrayof acoustic transducers 904, that given acoustic transducer generates acorresponding mechanical wave that can propagate through the adhesivelayer 906 into the acoustic medium 906 a, traversing a thickness of theacoustic medium 906 a until that mechanical wave reaches a surface ofthe acoustic medium 906 a that is generally opposite the first surfaceof the acoustic medium 906 a, after which at least a portion of theenergy of the mechanical wave is reflected from that second surface (theimaging surface). The reflected wave traverses the acoustic medium 906 aagain and may be received at least one sense-mode transducer.

As noted above, the depicted embodiment illustrates a depth-averaginglinear scan drive operation that leverages beamforming to focus acousticenergy emitted from multiple acoustic transducers at a selected locationof a curved imaging surface, focused to a particular depth. Moreparticularly, the application-specific integrated circuit 902 can beconfigured to select a scan plan that advances from one fractional areaof the imaging surface to another fractional area of the imaging surfaceonly after capturing information at different and/or varying depths ateach (or a selected number of) fractional area of the imaging surface.In this manner, the application-specific integrated circuit 902rasterizes an image of an object engaging the imaging surface, such as afingerprint of a user 908.

More specifically, in these examples, the application-specificintegrated circuit 902 can be configured to (1) select a fractional area910 a of the imaging surface, (2) select a scan plan and/or beamformingoperation that targets the fractional area 910 a, and (3) execute thatscan plan, such as shown in FIGS. 9A-9B.

In particular, as shown in FIG. 9A, a set of drive mode transducers anda set of sense mode transducers are selected from the array of acoustictransducers 904. In this embodiment, drive-mode transducers bookend(and/or circumscribe in a two-dimensional drive embodiment) thesense-mode transducers, but this is not required of all embodiments. Forreference and example, a sense mode transducer 912 is identified andbookended by drive-mode transducers 914 and 916. As with otherembodiments described herein, although only a single sense modetransducer is labeled, it may be appreciated that more than onetransducer can be operated in a sense mode. Similarly, although only twodrive-mode transducers are labeled, it may be appreciated that more thantwo transducers can be operated in a drive mode.

FIG. 9A depicts the drive-mode transducers 914 and 916 emitting acousticenergy (alongside, and timed with respect to adjacent and/or otherdrive-mode transducers) with specific timing such that a signal emittedfrom the drive-mode transducer 914 arrives at the selected fractionalarea of the imaging surface, the fractional area 910 a, at the same timethat a signal emitted from the drive-mode transducer 916 arrives. As aresult of this construction, reflections from these two signals mayconstructively interfere toward the direction of the sense-modetransducer 912, thereby increasing a signal-to-noise ratio associatedwith operated and/or receiving signals from the sense-mode transducer912.

FIG. 9B depicts the scan plan of FIG. 9A advanced by a step. Inparticular, FIG. 9B depicts the drive-mode transducers 914 and 916emitting acoustic energy (alongside, and timed with respect to adjacentand/or other drive-mode transducers) with specific timing such that asignal emitted from the drive-mode transducer 914 arrives at the sameselected fractional area of the imaging surface, but focused at a depthbeyond an interface between the acoustic medium 906 a and the user'sfinger 908. This focal point, identified as the fractional area 910 b,at the same time that a signal emitted from the drive-mode transducer916 arrives. As described above in reference to FIG. 9A, as a result ofthis construction, reflections from these two signals may constructivelyinterfere toward the direction of a sense-mode transducer 912, therebyincreasing a signal-to-noise ratio associated with operated and/orreceiving signals from the sense-mode transducer 912. In this example,as with other embodiments described herein, timings associated withdriving and/or sensing by the application-specific integrated circuit902 may be varied with respect to the operation shown in FIG. 9A due tocurvature of the acoustic medium 906 a.

In these examples, different samples taken at different depths may beaveraged and/or otherwise combined to output a single result for a givenfractional area of the input surface.

As described above, linear scan operations, whether those operations areperformed with or without depth-averaging, are not the only beamformingoperations that can be associated with a scan plan such as describedherein. For example, FIGS. 10A-10C depict a simplified cross-section ofan acoustic imaging system as described herein, implementing a sweepscan drive operation that leverages beamforming to focus acoustic energyemitted from multiple acoustic transducers at a set of selectedlocations of a curved imaging surface.

In the illustrated embodiment, an acoustic imaging system 1000 is shown.The acoustic imaging system 1000 includes an application-specificintegrated circuit 1002 that may be communicably, conductively, and/ormechanically coupled to an array of acoustic transducers 1004. As withother embodiments describe herein, the application-specific integratedcircuit 1002 of the acoustic imaging system 1000 can be configured toperform or coordinate one or more drive or sense operations of theacoustic imaging system 1000. The application-specific integratedcircuit 1002 can be configured and operated as described above withreference to other embodiments; this description is not repeated.

The acoustic imaging system 1000 also includes an adhesive layer 1006that acoustically and mechanically couples the array of acoustictransducers 1004 to a first surface of an acoustic medium 1006 a, whichhas a curved profile. As with other embodiments described herein, acurved profile is not required of all embodiments; some examples includeacoustic media of different cross-sectional profiles.

As a result of this construction, as with other embodiments describedherein, once the application-specific integrated circuit 1002 applies anappropriate voltage signal to a given acoustic transducer of the arrayof acoustic transducers 1004, that given acoustic transducer generates acorresponding mechanical wave that can propagate through the adhesivelayer 1006 into the acoustic medium 1006 a, traversing a thickness ofthe acoustic medium 1006 a until that mechanical wave reaches a surfaceof the acoustic medium 1006 a that is generally opposite the firstsurface of the acoustic medium 1006 a, after which at least a portion ofthe energy of the mechanical wave is reflected from that second surface(the imaging surface). The reflected wave traverses the acoustic medium1006 a again and may be received at least one sense-mode transducer.

As noted above, the depicted embodiment illustrates a sweep scan driveoperation that leverages beamforming to focus acoustic energy emittedfrom multiple acoustic transducers at a selected location of a curvedimaging surface. Thereafter, the same set of drive-mode transducersand/or the same set of sense-mode transducers can be used with differenttimings and/or delay coefficients to image a different fractionalsection. In this manner, a beam formed by timing output from one or moredrive-mode transcoders can be “swept” across the imaging surface. Inthese examples, as may be appreciated by a person of skill in the art,higher resolution over the embodiment shown in FIGS. 8A-8C may beobtained, as effectively continuous measurements may be taken across theimaging surface.

More particularly, the application-specific integrated circuit 1002 canbe configured to select a scan plan that linearly advances from onefractional area of the imaging surface to another fractional area of theimaging surface merely by modifying timing of the same set of drive-modetransducers and sense-mode transducers. In this manner, theapplication-specific integrated circuit 1002 rasterizes an image of anobject engaging the imaging surface, such as a fingerprint of a user1008.

More specifically, in these examples, the application-specificintegrated circuit 1002 can be configured to (1) select a fractionalarea 1010 a of the imaging surface, (2) select a scan plan and/orbeamforming operation and/or set of delay coefficients associatedtherewith that targets the fractional area 1010 a, and (3) execute thatscan plan, such as shown in FIGS. 10A-10C.

In particular, as shown in FIG. 10A, a set of drive mode transducers anda set of sense mode transducers are selected from the array of acoustictransducers 1004. In this embodiment, drive-mode transducers bookend(and/or circumscribe in a two-dimensional drive embodiment) thesense-mode transducers, but this is not required of all embodiments. Forreference and example, a sense mode transducer 1012 is identified andbookended by drive-mode transducers 1014 and 1016. Although only asingle sense mode transducer is labeled, as with previous embodiments,it may be appreciated that more than one transducer can be operated in asense mode. Similarly, although only two drive-mode transducers arelabeled, it may be appreciated that more than two transducers can beoperated in a drive mode.

FIG. 10A depicts the drive-mode transducers 1014 and 1016 emittingacoustic energy (alongside, and timed with respect to adjacent and/orother drive-mode transducers) with specific timing such that a signalemitted from the drive-mode transducer 1014 arrives at the selectedfractional area of the imaging surface, the fractional area 1010 a, atthe same time that a signal emitted from the drive-mode transducer 1016arrives. As a result of this construction, reflections from thesemultiple signals may constructively interfere toward the direction ofthe sense-mode transducer 1012, thereby increasing a signal-to-noiseratio associated with operated and/or receiving signals from thesense-mode transducer 1012.

FIG. 10B depicts the scan plan of FIG. 10A advanced by a step. Inparticular, FIG. 10B depicts the drive-mode transducers 1014 and 1016emitting acoustic energy (alongside, and timed with respect to adjacentand/or other drive-mode transducers) with specific timing such that asignal emitted from the drive-mode transducer 1014 arrives at adifferent selected fractional area of the imaging surface, thefractional area 1010 b, at the same time that a signal emitted from thedrive-mode transducer 1016 arrives. As described above in reference toFIG. 10A, as a result of this construction, reflections from thesesignals may constructively interfere toward the direction of asense-mode transducer 1012, thereby increasing a signal-to-noise ratioassociated with operated and/or receiving signals from the sense-modetransducer 1012. In this example, timings associated with driving and/orsensing by the application-specific integrated circuit 1002 may bevaried with respect to the operation shown in FIG. 10A due to curvatureof the acoustic medium 1006 a.

FIG. 10C depicts the scan plan of FIGS. 10A-10B advanced by yet anotherstep. In particular, FIG. 10C depicts the drive-mode transducers 1014and 1016 emitting acoustic energy (alongside, and timed with respect to,adjacent and/or other drive-mode transducers) with specific timing suchthat a signal emitted from the drive-mode transducer 1014 arrives at adifferent selected fractional area of the imaging surface, thefractional area 1010 c, at the same time that a signal emitted from thedrive-mode transducer 1016 arrives. As described above in reference toFIGS. 10A-10B, as a result of this construction, reflections from thesetwo signals may constructively interfere toward the direction of asense-mode transducer 1012, thereby increasing a signal-to-noise ratioassociated with operated and/or receiving signals from the sense-modetransducer 1012. In this example, timings associated with driving and/orsensing by the application-specific integrated circuit 1002 may bevaried with respect to the operation shown in FIG. 10A due to curvatureof the acoustic medium 1006 a.

The foregoing embodiments depicted in FIGS. 10A-10C and the variousalternatives thereof and variations thereto are presented, generally,for purposes of explanation, and to facilitate an understanding ofvarious operations of an acoustic imaging system, such as describedherein. However, it will be apparent to one skilled in the art that someof the specific details presented herein may not be required in order topractice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions ofspecific embodiments are presented for the limited purposes ofillustration and description. These descriptions are not targeted to beexhaustive or to limit the disclosure to the precise forms recitedherein. To the contrary, it will be apparent to one of ordinary skill inthe art that many modifications and variations are possible in view ofthe above teachings.

For example, FIGS. 11A-11C depict a simplified cross-section of anacoustic imaging system as described herein, implementing an inversesweep scan drive operation that leverages beamforming to focus acousticenergy emitted from multiple acoustic transducers at a selected locationof a curved imaging surface. In this example embodiment, a sweepoperation such as described above with reference to FIGS. 10A-10C can beperformed in inverse; instead of sweeping which fractional area of theinput surface is targeted with a subsequent beamforming operations, inFIGS. 11A-11C, a selected fractional area can remain the same, whiledifferent sets of drive-mode and sense-mode transducers are selected foreach subsequent step of the scan plan.

More particularly, in the illustrated embodiment, an acoustic imagingsystem 1100 is shown. As with other embodiments, the acoustic imagingsystem 1100 includes an application-specific integrated circuit 1102that may be communicably, conductively, and/or mechanically coupled toan array of acoustic transducers 1104. As with other embodimentsdescribe herein, the application-specific integrated circuit 1102 of theacoustic imaging system 1100 can be configured to perform or coordinateone or more drive or sense operations of the acoustic imaging system1100. The application-specific integrated circuit 1102 can be configuredand operated as described above with reference to other embodiments;this description is not repeated.

The acoustic imaging system 1100 also includes an adhesive layer 1106that acoustically and mechanically couples the array of acoustictransducers 1104 to a first surface of an acoustic medium 1106 a, whichhas a curved profile. As with other embodiments described herein, acurved profile is not required of all embodiments; some examples includeacoustic media of different cross-sectional profiles.

As noted above, the depicted embodiment illustrates an inverse sweepscan drive operation that leverages beamforming to focus acoustic energyemitted from multiple acoustic transducers at a selected location of acurved imaging surface. Thereafter, a different set of drive-modetransducers and/or a different set of sense-mode transducers can be usedwith different timings and/or delay coefficients to image the samefractional section. In this manner, a beam formed by timing output fromone or more drive-mode transcoders can be “swept” across the array ofacoustic transducers. In these examples, as may be appreciated by aperson of skill in the art, higher resolution over the embodiment shownin FIGS. 8A-8C may be obtained, as effectively continuous measurementsmay be taken across the imaging surface.

More particularly, the application-specific integrated circuit 1102 canbe configured to select a scan plan that images the same one fractionalarea of the imaging surface in multiple ways and/or from multiple angles(e.g., three-dimensional sensing in some configurations) by modifyingthe set of drive-mode transducers and sense-mode transducers. In thismanner, the application-specific integrated circuit 1102 rasterizes animage of an object engaging the imaging surface, such as a fingerprintof a user 1108.

More specifically, in these examples, the application-specificintegrated circuit 1102 can be configured to (1) select a fractionalarea 1110 of the imaging surface, (2) select a scan plan and/orbeamforming operation and/or set of delay coefficients associatedtherewith that targets the fractional area 1110, and (3) execute thatscan plan, such as shown in FIGS. 11A-11C.

In particular, as shown in FIG. 11A, a set of drive mode transducers anda set of sense mode transducers are selected from the array of acoustictransducers 1104. In this embodiment, drive-mode transducers bookend(and/or circumscribe in a two-dimensional drive embodiment) thesense-mode transducers, but this is not required of all embodiments. Forreference and example, a sense mode transducer 1112 a is identified andbookended by drive-mode transducers 1114 a and 1116 a. Although only asingle sense mode transducer is labeled, as with previous embodiments,it may be appreciated that more than one transducer can be operated in asense mode. Similarly, although only two drive-mode transducers arelabeled, it may be appreciated that more than two transducers can beoperated in a drive mode.

FIG. 11A depicts the drive-mode transducers 1114 a and 1116 a emittingacoustic energy (alongside, and timed with respect to adjacent and/orother drive-mode transducers) with specific timing such that a signalemitted from the drive-mode transducer 1114 a arrives at the selectedfractional area of the imaging surface, the fractional area 1110, at thesame time that a signal emitted from the drive-mode transducer 1116 aarrives. As a result of this construction, reflections from thesemultiple signals may constructively interfere toward the direction ofthe sense-mode transducer 1112 a, thereby increasing a signal-to-noiseratio associated with operated and/or receiving signals from thesense-mode transducer 1112 a.

FIG. 11B depicts the scan plan of FIG. 11A advanced by a step. Inparticular, FIG. 11B depicts the drive-mode transducers 1114 b and 1116b emitting acoustic energy (alongside, and timed with respect toadjacent and/or other drive-mode transducers) with specific timing suchthat a signal emitted from the drive-mode transducer 1114 b arrives atthe fractional area 1110 at the same time that a signal emitted from thedrive-mode transducer 1116 b arrives. As described above in reference toFIG. 11A, as a result of this construction, reflections from thesesignals may constructively interfere toward the direction of asense-mode transducer 1112 b, thereby increasing a signal-to-noise ratioassociated with operated and/or receiving signals from the sense-modetransducer 1112 b. In this example, timings associated with drivingand/or sensing by the application-specific integrated circuit 1102 maybe varied with respect to the operation shown in FIG. 11A due tocurvature of the acoustic medium 1106 a.

FIG. 11C depicts the scan plan of FIGS. 11A-11B advanced by yet anotherstep. In particular, FIG. 11C depicts the drive-mode transducers 1114 cand 1116 c emitting acoustic energy (alongside, and timed with respectto, adjacent and/or other drive-mode transducers) with specific timingsuch that a signal emitted from the drive-mode transducer 1114 c arrivesat a the same fractional area of the imaging surface, the fractionalarea 1110, at the same time that a signal emitted from the drive-modetransducer 1116 c arrives. As described above in reference to FIGS.11A-11B, as a result of this construction, reflections from these twosignals may constructively interfere toward the direction of asense-mode transducer 1112 c, thereby increasing a signal-to-noise ratioassociated with operated and/or receiving signals from the sense-modetransducer 1112 c. In this example, timings associated with drivingand/or sensing by the application-specific integrated circuit 1102 maybe varied with respect to the operation shown in FIG. 11A due tocurvature of the acoustic medium 1106 a.

The foregoing embodiments depicted in FIGS. 11A-11C and the variousalternatives thereof and variations thereto are presented, generally,for purposes of explanation, and to facilitate an understanding ofvarious operations of an acoustic imaging system, such as describedherein. However, it will be apparent to one skilled in the art that someof the specific details presented herein may not be required in order topractice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions ofspecific embodiments are presented for the limited purposes ofillustration and description. These descriptions are not targeted to beexhaustive or to limit the disclosure to the precise forms recitedherein. To the contrary, it will be apparent to one of ordinary skill inthe art that many modifications and variations are possible in view ofthe above teachings.

For example, although the embodiments shown and described in referenceto FIGS. 8A-11C are shown in cross-section, it may be appreciated thatany beamforming operation as described herein can be performed withdrive-mode transducers arranged in a two-dimensional array.

In such examples, it may be preferred in some embodiments to optimizebeamforming timings based not on, or not exclusively on, arrival time ofacoustic pulses at an imaging surface or, in particular, a fractionalarea of the imaging surface, but rather it may be preferred to optimizebeamforming operations to minimize carrier noise received at sense-modetransducers after the acoustic signals emitted from drive-modetransducers has reflected from the surface of the acoustic medium (e.g.,reflected from the imaging surface).

It may be appreciated that such optimizations depend on a number offactors including an arrangement of drive-mode transducers for aparticular embodiment (and/or selected for a particular beamformingoperation), a location of the targeted fractional area of the inputsurface, a location of one or more sense-mode transducers, and so on. Asa result, optimization may be, in some cases, an implementation-specificoperation.

FIG. 12 depicts a system/signal flow diagram of a system for optimizingdelay coefficients of a drive mode of an acoustic imaging system asdescribed herein. The figure corresponds, generally, to an examplemethod of optimizing output from a given set of drive-mode transducersto reduce carrier noise at a sense-mode transducer. In anothernon-limiting phrasing, the method associated with the system/signal flowdiagram of FIG. 12 may optimize for destructive interference at orbefore one or more particularly-located sense-mode transducers.

In this example, a calibration operation 1200 can be performed in whicha given array of transducers 1202 is selected and from the array a setof sense-mode transducers are selected. In this example, the sense-modetransducers are generally in the center of the array of transducers1202, but it may be appreciated that this is merely one exampleconstruction and that other scan plans and/or other beamformingoperations may optimize differently.

In this example, the calibration operation 1200 stimulates eachdrive-mode transducer of the array individually, cycling through alldrive-mode transducers one at a time. Signals received from thesense-mode transducers can be provided as input to a vector networkanalyzer and/or a time domain reflectometer 1204. Either apparatus maybe leveraged to characterize timing and/or frequency-domain content ofthe signals received by the sense-mode transducers for each driveoperation of each drive-mode transducer.

Thereafter output from the vector network analyzer and/or a time domainreflectometer 1204 can be provided as input to an optimizer 1206 that,in accordance with one or more settings defined by or in a memory 1208,can optimize delays for each signal associated with each drive-modetransducer to minimize carrier output at the sense-mode transducers. Oneexample optimization array including delay coefficients for eachdrive-mode transducer is shown as the example delay coefficient array1210.

The foregoing embodiments depicted in FIG. 12 and the variousalternatives thereof and variations thereto are presented, generally,for purposes of explanation, and to facilitate an understanding ofvarious operations of an acoustic imaging system, such as describedherein. However, it will be apparent to one skilled in the art that someof the specific details presented herein may not be required in order topractice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions ofspecific embodiments are presented for the limited purposes ofillustration and description. These descriptions are not targeted to beexhaustive or to limit the disclosure to the precise forms recitedherein. To the contrary, it will be apparent to one of ordinary skill inthe art that many modifications and variations are possible in view ofthe above teachings.

FIG. 13 is a flowchart depicting example operations of a method ofoperating a thin-film acoustic imaging system, such as described herein.The method 1300 includes operation 1302 at which a fractional area of animaging surface is selected. Next at operation 1304 a scan plan suitablefor the fractional area and/or surrounding/adjacent areas is selected.Finally at operation 1306, the scan plan can be executed and one or morebeamforming operations can be performed.

FIG. 14 is a flowchart depicted example operations of a method ofoperating a thin-film acoustic imaging system, such as described herein.The method 1400 includes operation 1404 at which a set of transducersdefining an area is selected. At operation 1404, each of the transducerscan be driven individually. At operation 1406, reflections resultingfrom those drive operations can be received at sense-mode transducers.At operation 1408, reflections received at operation 1406 can bereceived as input to an optimization controller. Finally, at operation1410, beamsteering and/or beamforming operations can be optimized toreduce carrier amplitude at sense-mode transducers.

One may appreciate that although many embodiments are disclosed above,that the operations and steps presented with respect to methods andtechniques described herein are meant as exemplary and accordingly arenot exhaustive. One may further appreciate that alternate step order orfewer or additional operations may be required or desired for particularembodiments.

Although the disclosure above is described in terms of various exemplaryembodiments and implementations, it should be understood that thevarious features, aspects and functionality described in one or more ofthe individual embodiments are not limited in their applicability to theparticular embodiment with which they are described, but instead can beapplied, alone or in various combinations, to one or more ofembodiments, whether or not such embodiments are described and whetheror not such features are presented as being a part of a describedembodiment. Thus, the breadth and scope of the claimed subject mattershould not be limited by any of the above-described exemplaryembodiments but is instead defined by the claims herein presented.

The present disclosure recognizes that personal information data,including biometric data, in the present technology, can be used to thebenefit of users. For example, the use of biometric authentication datacan be used for convenient access to device features without the use ofpasswords. In other examples, user biometric data is collected forproviding users with feedback about their health or fitness levels.Further, other uses for personal information data, including biometricdata, that benefit the user are also contemplated by the presentdisclosure.

The present disclosure further contemplates that the entitiesresponsible for the collection, analysis, disclosure, transfer, storage,or other use of such personal information data will comply withwell-established privacy policies and/or privacy practices. Inparticular, such entities should implement and consistently use privacypolicies and practices that are generally recognized as meeting orexceeding industry or governmental requirements for maintaining personalinformation data private and secure, including the use of dataencryption and security methods that meets or exceeds industry orgovernment standards. For example, personal information from usersshould be collected for legitimate and reasonable uses of the entity andnot shared or sold outside of those legitimate uses. Further, suchcollection should occur only after receiving the informed consent of theusers. Additionally, such entities would take any needed steps forsafeguarding and securing access to such personal information data andensuring that others with access to the personal information data adhereto their privacy policies and procedures. Further, such entities cansubject themselves to evaluation by third parties to certify theiradherence to widely accepted privacy policies and practices.

Despite the foregoing, the present disclosure also contemplatesembodiments in which users selectively block the use of, or access to,personal information data, including biometric data. That is, thepresent disclosure contemplates that hardware and/or software elementscan be provided to prevent or block access to such personal informationdata. For example, in the case of biometric authentication methods, thepresent technology can be configured to allow users to optionally bypassbiometric authentication steps by providing secure information such aspasswords, personal identification numbers (PINS), touch gestures, orother authentication methods, alone or in combination, known to those ofskill in the art. In another example, users can select to remove,disable, or restrict access to certain health-related applicationscollecting users' personal health or fitness data.

What is claimed is:
 1. An electronic device comprising: a housing; andan acoustic imaging system coupled to the housing, defining an imagingsurface on an exterior surface of the housing, and comprising: an arrayof thin-film acoustic transducers each operable in a drive mode and asense mode; a scan planner coupled to the array and configured to:select a fractional area of the imaging surface; select a scan plancomprising: a first set of thin-film acoustic transducers selected fromthe array of thin-film acoustic transducers and operated in drive mode;a second set of thin-film acoustic transducers selected from the arrayof thin-film acoustic transducers and operated in sense mode; and a setof delay coefficients, each coefficient defining a delay after which acorresponding one thin-film acoustic transducer of the first set ofthin-film acoustic transducers generates a drive signal; and execute theselected scan plan to cause each thin-film acoustic transducers of thefirst set of thin-film acoustic transducers to generate a respective onedrive signal delayed according to a respective one coefficient of theset of delay coefficients; an analog to digital converter stageconfigured to receive at least one electrical signal from the second setof thin-film acoustic transducers and to output a digital valuecorresponding to acoustic impedance mismatch at the fractional area; andan image processor configured to: receive as input the digital valuefrom the analog to digital converter; and provide as output an image ofan object engaging the imaging surface, the image comprising a pixelbased at least in part on the digital value.
 2. The electronic device ofclaim 1, wherein the exterior surface of the housing has a curvedprofile.
 3. The electronic device of claim 2, wherein the scan plan isselected, at least in part, based on the curved profile.
 4. Theelectronic device of claim 3, wherein the set of delay coefficients isbased at least in part on the curved profile of the housing.
 5. Theelectronic device of claim 1, wherein the electronic device is awearable electronic device and the acoustic imaging system is coupled toa sidewall of the housing.
 6. The electronic device of claim 1, whereinthe first set is disjoint with the second set.
 7. The electronic deviceof claim 1, wherein the scan plan is selected from a set of scan plans.8. The electronic device of claim 1, wherein the set of delaycoefficients is optimized to reduce carrier noise at the second set ofthin-film acoustic transducers.
 9. The electronic device of claim 1,wherein the housing is formed from metal and has a curved profile suchthat the imaging surface is curved, contouring to the curved profile.10. The electronic device of claim 9, wherein the metal is titanium orstainless steel.
 11. An acoustic imaging system for biometric imagingthrough a housing of a portable electronic device, the acoustic imagingsystem comprising: an array of thin-film acoustic transducersacoustically coupled to an interior sidewall surface of the housing,thereby defining an imaging surface along an exterior surface of thehousing; a scan planner coupled to the array and configured to execute ascan plan defining a relative drive mode delay between at least twothin-film acoustic transducers of the array to direct acoustic energy toa selected fractional area of the imaging surface; an analog to digitalconverter stage configured to receive at least one electrical signalfrom at last one thin-film acoustic transducer of the array of thin-filmacoustic transducers and to output a digital value corresponding to anacoustic impedance mismatch at the selected fractional area; and animage processor configured to provide as output an image of an objectengaging the imaging surface, the image comprising a pixel based atleast in part on the digital value.
 12. The acoustic imaging system ofclaim 11, wherein the image comprises a fingerprint image.
 13. Theacoustic imaging system of claim 11, wherein the exterior surface andthe imaging surface are at least partially curved.
 14. The acousticimaging system of claim 11, wherein at least one thin-film acoustictransducer of the array of thin-film acoustic transducers is formed fromPVDF.
 15. The acoustic imaging system of claim 11, wherein the imagingsurface is defined at least partially through one of a button or arotary input device.
 16. A method of executing a scan plan for animaging area defined by an acoustic imaging system coupled to a housingof an electronic device, the method comprising: selecting, from an arrayof acoustic transducers operable in a drive mode and a sense mode, afirst set of acoustic transducers to operate in the drive mode;selecting, from the array of acoustic transducers, a second set ofacoustic transducers to operate in the sense mode; selecting a scanplan; and providing, as output, an image of an object engaging theimaging surface, the image comprising at least one pixel based on atleast one digital value generated by iteratively selecting a targetfractional area of the imaging area and: driving the first set ofacoustic transducers according to a set of delay coefficients defined bythe scan plan and based on the target fractional area; receiving, fromthe second set of acoustic transducers, at least one electrical signalto be converted to a digital value corresponding to acoustic impedanceat the target fractional area of the imaging area; and selecting a nexttarget fractional area as the target fractional area.
 17. The method ofclaim 16, wherein the first set of acoustic transducers circumscribesthe second set of acoustic transducers.
 18. The method of claim 16,wherein at least one acoustic transducer of the array of acoustictransducers comprises a thin-film piezoelectric actuator.
 19. The methodof claim 16, wherein the housing is formed from metal and has a curvedprofile.
 20. The method of claim 16, wherein the first set of acoustictransducers defines a contiguous area of acoustic transducers.